"Virgin Cross Country are attempting to claw back some of the cost of introducing the 35-hour week by undermining rates for working on Sundays," RMT general secretary Bob Crow said today.

"Our 35-hour week agreement was supposed to have brought us a shorter working week without loss of pay, but the value of Sunday enhancements has been slashed by nearly six per cent.

"The result is that our members are being expected to give up their Sundays for a smaller premium - and that makes a mockery of the agreement we reached with the company.

"It is not as if we are talking about a huge sum of money - our claim amounts to less than £6 a shift.

"To add insult to injury the company has begun treating Sunday rosters as if they are compulsory, despite our agreement that Sundays remain outside the normal working week.

"We have tried to negotiate a settlement with the company but Virgin Cross Country has simply refused to offer any improvements and we are left with no choice but to strike on Sunday January 1.

"The company can settle this dispute by restoring the full value of Sunday pay rates, but if they do not they face the prospect of our members stopping work every Sunday," Bob Crow said.