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Secondary action (also known as a secondary boycott or sympathy strike) is industrial action by a trade union in support of a strike initiated by workers in another, separate enterprise. The term "secondary action" is intended to be distinct from a trade dispute with a worker's direct employer, and so may be used to refer to a dispute with the employer's parent company, its suppliers, financiers, contracting parties, or any other employer in another industry.
In most countries there are limits on the purpose for which people can go on strike, and in many English speaking nations restrictions have been placed on which organisations trade unions may strike against. In the US and UK workers can typically strike against their direct employer only. In continental Europe, secondary action is generally lawful and the right to strike is seen as a part of broader political freedom.
In Australia it is banned by sections 45D to 45E of the Trade Practices Act. In the 1910s, sympathy strikes were sometimes called in order to extend a strike beyond the bounds of any one Australian state, thus making it eligible for handling by the Federal Arbitration Court.
United Kingdom 
In the United Kingdom, sympathy strikes were outlawed by the Trade Disputes and Trade Union Act of 1927 in the aftermath of the General Strike. This was repealed by the Trade Disputes and Trade Unions Act 1946, passed by the post-war Labour Government.
Secondary action remained legal until 1980, when the Conservative Government of Margaret Thatcher passed the Employment Act 1980 which restricted secondary action. This was followed a decade later by the Employment Act 1990, which outlawed secondary action entirely. The laws outlawing secondary strikes remain to this day. In 2005, union leaders in the U.K. called for the legalisation of secondary strikes in the aftermath of the strike action against the catering company Gate Gourmet but Labour ministers stated that they had no intention of repealing the law.
- National Sailors’ and Firemen's Union v Reed  Ch 536
- Express Newspapers ltd v MacShane  ICR 42
- Duport Steel Ltd v Sirs  ICR 161
United States 
Secondary action is illegal in the United States. It is banned by the Sherman Antitrust Act and by the Taft-Hartley Act, which amends the National Labor Relations Act of 1935 (also known as the Wagner Act).
Because farm laborers in the United States are not covered by the Wagner Act, the United Farm Workers union has been able to legally use secondary boycotting of grocery store chains as an aid to their strikes against California agribusinesses and to their primary boycotts of California grapes, lettuce and wine. The UFW's secondary boycotts involved asking consumers to stop shopping at a grocery store chain until such time as the chain stopped carrying the boycotted grapes or lettuce or wine.
Secondary boycotting is frequently confused with secondary striking, which is also a prohibited tactic for those labor unions covered by the Taft-Hartley Act. Some legal definitions for secondary boycotting divide it into two different kinds, secondary consumer boycotts as per the above definition of secondary boycotts, and secondary employee boycotts, also defined as a secondary strike.
See also 
- M Kite and T Freinberg, 'Unions to Challenge Blair Over Ban on Secondary Strikes' (Daily Telegraph, 27 August 2005).