In ten key test cases today, more than pounds 95m worth of backdated pension benefits will be claimed on behalf of 60,000 part-time staff - the overwhelming majority of whom are women.
Citing a European Court ruling last September, lawyers will argue that the employees in local government, the health service, education and high street banks were the victims of sex discrimination by being excluded from pension schemes.
The lawyers are seeking to backdate benefits to 1976, when the European Court of Justice gave a key ruling in favour of part-timers' rights.
Under an amendment to the Pension Schemes Act, last May, the limit on claims was only extended back two years, to May 1993.
Employers at today's hearing at a Birmingham industrial tribunal will contend that benefits should not be backdated further, while the TUC will argue that the tribunal has the legal power to make its own judgement.
The TUC, which has co- ordinated the cases on behalf of its own affilates and independent staff associations, calculates that the total compensation involved could amount to more than pounds 95m. It believes that such a sum is affordable because the pension fund assets involved stand at more than pounds 500bn.
The TUC's backing for the cases forms part of its two-year campaign to win pro rata rights to pay and conditions for Britain's 5 million part- timers.
John Monks, the General Secretary of the TUC, said employers would have to wake up to the fact that part-time workers should be treated the same as full-timers.
According to the latest Labour Force Survey, there are 5.4m part-time workers in Britain, of whom 4.7m are women. The TUC estimates that only about 850,000 of them are in occupational pensions schemes, but that another 3 million are now eligible.