Private sector union Amicus will launch a major investigation in the New Year into breaches of the working time regulations among rail maintenance companies, after securing an out-of-court settlement in excess of £500,000 for workers.
The union said cheques for retrospective payments are being sent out to 282 rail maintenance workers in time for Christmas.
The investigation has been prompted by revelations that the GTBB joint venture project, whose sponsor companies are Balfour Beatty and Carillion, had failed to pay a number of staff their holiday pay in compliance with the working time directive.
The union is gathering evidence to demonstrate that these are not isolated incidents but part of a widespread practice among maintenance companies.
Rail staff across the UK could be losing up to £1,500 a year because companies do not to calculate holiday pay properly, the union said.
Until August 2003 the rail industry was exempt from the regulations.
The union will investigate pay practices across the rail industry following revelations that a number of companies calculate holiday pay based on basic salary only, rather than including retention bonuses, shift premiums and shift allowances as the working time regulations require.
The union believes this week's settlement for 280 employees is only the tip of the iceberg.
Bob Rixham, national officer, transport, said: "Rail maintenance companies will be best advised to review their holiday payment policies or they will be pursued to a tribunal."