Mastro Plastics Corp. et al. v. National Labor Relations Board
The court held that, when an employer has committed an unfair labor practice, strikes in protest of that practice are protected by the National Labor Relations Act even when the collective bargaining agreement includes a no-strike clause.
350 U.S. 270 · No. 19 · 1955 term · Warren Court
Decided Feb 27, 1956 · argued Oct 17, 1955
Unions · Labor-management disputes: no-strike clause
Majority opinion: Harold Burton
The voteMajorityDissent
6–36 in the majority, 3 in dissent
3 dissents (6–3)
Affirmed. Mastro Plastics Corp. et al. lost.
What this ruling means
Affirmed: the Supreme Court upheld the decision of the U.S. Court of Appeals, Second Circuit, so it stands (sometimes with changes the Court made to it).
Mastro Plastics Corp. et al. was the petitioner, the side that asked the Supreme Court to review the case. “Lost” means the Court did not give that side the result it asked for.
From the Supreme Court Database. A justice who agreed with the result but not the reasoning counts in the majority.
Summary
The opening of the case’s Wikipedia article: what the case was about and what the Court held.
Mastro Plastics Corporation v. National Labor Relations Board, 350 U.S. 270 (1956), was a United States Supreme Court case in which the court held that, when an employer has committed an unfair labor practice, strikes in protest of that practice are protected by the National Labor Relations Act even when the collective bargaining agreement includes a no-strike clause.
Data notes
The text is Wikipedia’s (CC BY-SA 4.0), matched to the case by its citation, docket number or name and year, and is not checked against the opinion. The site keeps the article’s opening section, ending on its last full sentence. The one-sentence summary under the title is the Decisions list’s: Wikipedia’s own ruling sentence, or, tagged “AI-written”, one Claude wrote from this opening.
How the justices voted
Each justice who took part, placed by their Martin–Quinn ideology score for the 1955 term. Filled: the 6 in the majority. Hollow: the 3 in dissent. Colour is the party of the president who appointed them.
Majority(6)
Harold BurtonWrote the majority opinion
William DouglasJoined the majority
Hugo BlackJoined the majority
Earl WarrenJoined the majority
Tom ClarkJoined the majority
Stanley ReedJoined the majority
Dissent(3)
Felix FrankfurterWrote a dissent
Sherman MintonJoined a dissent
John HarlanJoined a dissent
Data notes
Each justice’s vote and what they wrote are from the justice-centered file of the Supreme Court Database. “Wrote a concurrence” means the justice sided with the majority and wrote separately; a justice who dissented in part is counted on the side they took overall. A justice who wrote nothing is listed as joining their side.
Positions are each justice’s Martin–Quinn score for the case’s term, the same scores as the Ideology page: negative is more liberal, positive more conservative. A score sums up a justice’s votes across the whole term, so it says where they usually sit, not why they voted as they did here. The median line is the Court’s median justice that term.
The parties
Who brought the case to the Court, who answered it, and how it got there.
- Petitioner
- Mastro Plastics Corp. et al.Employer
- Respondent
- National Labor Relations BoardNational Labor Relations Board, or regional office or officer
- Reached the Court by
- Certiorari (the Court chose to hear it)
Data notes
The names are the two sides of the case’s title. The description under each is the Supreme Court Database’s category for that party, in its own wording. The petitioner is the side that asked the Supreme Court to review the decision below. “Why it was taken” appears only when the majority opinion says lower courts disagreed or were unsure about the question; reasons that would fit any case (“to resolve the question presented”, “an important question”) are left out.
The law at issue
The law the Court was asked to apply, and the kind of power it used to decide.
- Provision
- National Labor Relations, as amended
- Kind of law
- Federal Statute
- Decided by
- Interpretation of administrative regulation or rule, or executive order; Statutory construction
Data notes
The Supreme Court Database codes the main constitutional provision, statute or court rule each case turned on, and the basis of the decision: judicial review of a federal or state law, interpreting a statute, supervising the lower courts, and so on. A case can rest on more than one. “Overruled” counts only where the majority opinion says so.
Timeline
What happened at the Court and how the case got there, newest first.
- Feb 27, 1956DecidedDecided · Decided 6–3: affirmed. Mastro Plastics Corp. et al. lost.
- Oct 17, 1955ArguedArgued · Oral argument before the Court.
- Not datedTaken upTaken up · The Supreme Court agreed to hear the case (certiorari).
- Not datedCourt belowCourt below · Began in and was decided by the U.S. Court of Appeals, Second Circuit: affirmed, with a dissent.
Data notes
From the Supreme Court Database: the court the case began in, the court whose decision the Supreme Court reviewed and what that court did, how the case came to the Court, and the dates of argument and decision. The database does not date the steps in the lower courts. Court names are the database’s.
Other decisions on the same issue
7 other argued cases since 1946 on labor-management disputes: no-strike clause, newest first.
- Metropolitan Edison Co. v. National Labor Relations Board et al.460 U.S. 693Apr 4, 1983 · 460 U.S. 693Unions9–0Unanimous band
- Complete Auto Transit, Inc., et al. v. Reis et al.451 U.S. 401May 4, 1981 · 451 U.S. 401Unions7–27–2 band
- Carbon Fuel Co. v. United Mine Workers of America et al.444 U.S. 212Dec 10, 1979 · 444 U.S. 212Unions9–0Unanimous band
- Gateway Coal Co. v. United Mine Workers of America et al.414 U.S. 368Jan 8, 1974 · 414 U.S. 368Unions8–18–1 band
- Atkinson et al. v. Sinclair Refining Co.370 U.S. 238Jun 18, 1962 · 370 U.S. 238Unions8–0Unanimous band
- Local 174, Teamsters, Chauffeurs, Warehousemen & Helpers of America, v. Lucas Flour Co.369 U.S. 95Mar 5, 1962 · 369 U.S. 95Unions8–18–1 band
- Brotherhood of Railroad Trainmen et al. v. Chicago River & Indiana Railroad Co. et al.353 U.S. 30Mar 25, 1957 · 353 U.S. 30Unions8–0Unanimous band
Data notes
Every other orally argued case with a clear vote, from the 1946 term on, that the Supreme Court Database files under the same issue as this one. The database gives each case one issue from a list of about 270 (abortion, search and seizure of vehicles, the death penalty, and so on), whatever law it turned on.
Official record
Read the full opinion on Justia, the argument audio on Oyez and Wikipedia. Case data from the Supreme Court Database, Version 2026 Release 01, through the 2025 term.