The court backed complaints brought by an employee of the Daily Mail and a docker from Southampton who said they had been unfairly penalised for failing to sign individual contracts derecognising their unions.
Lawyers said the ruling would force companies to 'tread very carefully' if they wanted to follow the increasingly common practice of tearing up collective agreements and negotiating with employees individually.
Firms can still derecognise trade unions and alter the conditions of their workers' contracts, the court said. But Lord Justice Dillon, sitting with Lords Justice Butler-Sloss and Farquharson, said managers were not entitled to offer douceurs to employees who supported derecognition while excluding those who did not.
The judgment, described by trade unionists as hugely significant, came as David Wilson, a sub-editor at the Daily Mail, and Brian Stedman, a bosun with Associated British Ports, appealed against a decision by the Employment Appeal Tribunal, which had rejected their complaints.
Mr Wilson, head of the National Union of Journalists' chapel at the Daily Mail, said his employers had acted illegally when they denied him and 12 colleagues a 4.5 per cent pay rise for refusing to sign personal contracts in 1990. Mr Wilson says he has lost pounds 5,000 since then.
In a similar claim, Mr Stedman said he had lost pounds 20 a week by failing to sign an individual agreement in 1991.
Both men said their employers had intended to discriminate against them because they were union members, but this was illegal under the 1978 Employment Protection (Consolidation) Act. The firms were refused leave to appeal to the House of Lords, although they can still seek permission to do so from the Law Lords themselves.
John Hendy QC, for Mr Wilson, said later: 'This is one of the most important judicial decisions for trade unionists of the century. It is the first time that companies trying to end bargaining with unions representing their staff have been stopped in their legal tracks.'Reuse content