Strikebreaker | HR Glossary

A strikebreaker is a person who works during a labor strike, either by continuing employment as a non-striking worker or by being newly hired to replace a striking employee.

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Strikebreaker (also called a replacement worker) is a person who works during a labor strike — either continuing employment as a non-striking employee or being newly hired to replace a striking worker. The neutral legal term under U.S. labor law is replacement worker; “scab” is a pejorative union term with no formal legal definition. Governed by the National Labor Relations Act (NLRA) and the Mackay Radio doctrine (1938).

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What is a strikebreaker?

A replacement worker fills a striking employee’s role during a work stoppage. That includes external hires recruited for the strike period, supervisors temporarily redeployed to production roles, employees from other facilities reassigned within the same company, and contractors engaged for the duration.

The term “professional strikebreaker” refers to individuals or firms specializing in replacement labor for labor disputes. Several states — including Oregon, Michigan, and New York — restrict or prohibit the use of professional strikebreakers by statute.

Legal framework: NLRA and the right to strike

The National Labor Relations Act (29 U.S.C. ss 151-169) governs labor relations for most private-sector employers in the United States. Two provisions define the core framework:

Section 7 gives employees the right to organize, engage in collective bargaining, and take part in other concerted activities, including the right to strike.
Section 13 protects the right to strike from limitation except as specifically provided in the Act.

Within that framework, the NLRB draws a decisive distinction between economic strikes and unfair labor practice (ULP) strikes. The rules for replacement workers differ sharply between the two types.

Economic strikes vs unfair labor practice strikes

Factor	Economic strike	ULP strike
Cause	Wages, hours, working conditions	Employer NLRA violation (bad-faith bargaining, retaliation)
Permanent replacement allowed?	Yes (Mackay Radio doctrine)	No
Reinstatement when strike ends	Preferential recall list; not automatic	Unconditional — must reinstate even if replacements are terminated
Misclassification risk	Back pay owed to every striker from date reinstatement should have occurred	—

An economic strike is a work stoppage over wages, hours, benefits, or terms of employment. A ULP strike is triggered by the employer’s own NLRA violation. Before deploying any permanent replacement workers, labor counsel must confirm the strike classification in writing.

The mackay radio doctrine

The foundational precedent is NLRB v. Mackay Radio and Telegraph Co., 304 U.S. 333 (1938). The Supreme Court held three things:

Workers who strike remain “employees” under the NLRA and cannot be permanently fired for striking.
An employer facing an economic strike may hire replacement workers and is not required to discharge permanent replacements when the strike ends.
If replacements were hired with a promise of permanent employment, the employer may give them preference over returning strikers.

Economic strikers who are permanently replaced are not entitled to immediate reinstatement. They go on a preferential recall list and must be offered their jobs back when a qualifying vacancy arises, provided they have not found substantially equivalent employment and have made an unconditional offer to return.

The Mackay doctrine remains controlling federal law.

Rights of replacement workers

Replacement workers hired during a strike hold the following protections:

Wages and conditions: Entitled to the wages and working conditions offered at hire.
No mandatory union membership: Cannot be compelled to join the union; Section 7 protects the right to refrain from union activity.
NLRA protection: Replacement workers are “employees” under the NLRA and retain rights to organize or engage in concerted activity.
Job security: Permanent replacements have a greater expectation of continued employment than temporary replacements.
Safety protections: All OSHA obligations apply identically to replacement workers and regular employees.

Employer rights and limits

Employers may:

Continue operations using replacement workers
Hire permanent replacements for economic strikers (Mackay doctrine)
Reassign supervisory and managerial staff to production roles
Communicate factual information about the dispute to employees and replacements

Employers may not:

Discriminate against employees for union activity, including striking (Section 8(a)(3))
Promise benefits to strikers to induce them to abandon the strike (Section 8(a)(1))
Surveil or photograph picketers in a manner that creates reasonable fear of reprisal
Hire permanent replacements for unfair labor practice strikers

Reinstatement rights for striking workers

Economic strikers replaced by temporary workers are entitled to reinstatement as positions open up. Economic strikers replaced by permanent workers are placed on a preferential recall list and must be offered the next available qualifying vacancy.

ULP strikers are entitled to unconditional reinstatement when the strike ends, even if replacement workers must be displaced. Back pay accrues from the date the striker made an unconditional offer to return.

Misconduct exception: Strikers who engaged in serious misconduct during the strike may be lawfully denied reinstatement.

Historical context

The practice predates federal labor law: 19th-century employers routinely brought in replacement workers under armed escort, often using private security firms like the Pinkerton Agency, with little regulatory constraint. The Wagner Act (1935) established the NLRA framework, and the Mackay Radio decision (1938) set the legal boundary that governs replacement worker practice today.

Strike contingency planning for HR teams

A strike is a business continuity event. Planning must start during contract negotiations, not after impasse is declared. SHRM recommends tracking grievance trends and monitoring union communications as leading indicators.

1. Strike risk assessment: Identify contracts expiring within 12-18 months. Early signals include work-to-rule slowdowns and increased grievance filings.

2. Operational triage: Categorize every role by criticality. Determine which functions management can cover, which require external replacement workers, and which can be suspended.

3. Legal review: Confirm strike classification rules with labor counsel, establish compliant communication protocols, and document the operational basis for any permanent replacement decisions.

4. Replacement worker sourcing: Identify staffing agencies with labor dispute experience before a dispute begins. Screen vendors against state-level professional strikebreaker restrictions.

5. Rapid screening and skills verification: Speed matters when deploying replacement workers. A structured assessment verifies technical skills, safety knowledge, and role competencies before workers enter critical functions.

6. Documentation: Record every replacement hiring decision including permanent-vs-temporary designation. This is essential if NLRB investigation follows or reinstatement disputes arise.

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Screening replacement workers quickly

Skills assessments give HR teams a structured, auditable screening method when time is compressed:

Role-specific skills tests verify candidates can perform the function — critical for safety-sensitive or technical roles.
Cognitive ability assessments predict learning speed, which matters when onboarding happens in hours rather than weeks.
Structured scoring creates an objective, documented basis for hiring decisions, protecting against discrimination claims under NLRA Section 8(a)(3).

Testlify’s skills assessments cover 3,000+ competencies across operations, manufacturing, logistics, healthcare administration, and professional services.

Key terms

Term	Definition
Strikebreaker	Person who works during a strike, either continuing employment or newly hired to replace strikers
Economic strike	Strike over wages, hours, or conditions — permits permanent replacement under Mackay
ULP strike	Strike protesting an employer NLRA violation — does not permit permanent replacement
Mackay Radio doctrine	1938 Supreme Court precedent permitting permanent replacement of economic strikers
Preferential recall	Obligation to offer returning economic strikers the next available qualifying vacancy

Frequently asked questions

A strikebreaker is a person who works during a labor strike, either by continuing employment as a non-striking worker or by being newly hired to replace a striking employee. The neutral legal term is “replacement worker.” Under the National Labor Relations Act, hiring replacement workers during an economic strike is lawful for most private-sector employers in the United States.

Yes, for most private-sector employers under federal law. The NLRA permits employers to hire replacement workers during an economic strike, including permanent replacements under the Mackay Radio doctrine. For ULP strikes, replacements may be hired but cannot be permanent, and strikers must be reinstated unconditionally when the strike ends. State laws may add restrictions, particularly on professional strikebreaker agencies.

An economic strike is a work stoppage over wages, hours, benefits, or terms of employment. A ULP strike is triggered by the employer committing an NLRA violation — such as refusing to bargain in good faith or retaliating against union organizers. Economic strikers can be permanently replaced; ULP strikers cannot. Misclassifying a ULP strike as economic and hiring permanent replacements can result in mandatory reinstatement of all strikers plus back pay.

The Mackay Radio doctrine comes from the Supreme Court’s 1938 decision in NLRB v. Mackay Radio and Telegraph Co., 304 U.S. 333. The Court held that an employer in an economic strike may hire permanent replacement workers and is not required to dismiss them when the strike ends. Economic strikers who are permanently replaced retain employee status and go on a preferential recall list, but are not entitled to immediate reinstatement.

It depends on whether they were hired as permanent or temporary replacements. Permanent replacements have a contractual expectation of continued employment under the Mackay Radio doctrine. For ULP strikes, the employer must reinstate strikers unconditionally when the strike ends, which may require terminating replacement workers.

Economic strikers temporarily replaced are entitled to reinstatement as positions open. Those permanently replaced go on a preferential recall list and must be offered the next qualifying vacancy, provided they have made an unconditional offer to return. ULP strikers are entitled to immediate reinstatement when the strike ends, even if replacement workers must be displaced. Strikers who engaged in serious misconduct during the strike may be lawfully denied reinstatement.

Employers can develop contingency plans and pre-screen candidates, but actively hiring replacements before a strike is called may violate the NLRA. The NLRB has found that pre-strike replacement hiring timed to chill union activity violates Section 8(a)(1) and 8(a)(3). Best practice: engage labor counsel before recruiting, establish a documented operational trigger (such as receipt of a formal strike notice), and do not advertise replacement positions before the strike has commenced.

Standard multi-week hiring timelines are not viable during a strike. Enterprise HR teams use skills assessments to verify technical competence, cognitive ability, and role fit in hours. Structured scoring also creates an objective, documented basis for hiring decisions, protecting against discrimination claims under NLRA Section 8(a)(3). Testlify’s assessment library covers 3,000+ skills across operations, manufacturing, logistics, and professional services. Start a free trial to build a contingency assessment workflow.