Drivers on London Underground are to vote on industrial action in a row over Boxing Day pay, threatening fresh disruption on the Tube, it was learned today.
Aslef said LU was insisting that December 26 was a normal working day, but the union said its members should receive additional pay.
"To claim that Boxing Day is an ordinary working day is an almost unbelievable denial of an obvious fact. They are living on another planet if they think Aslef members will accept this piece of fiction," said one Aslef official.
The union said it had argued the case for additional payments for working on Boxing Day at a number of meetings with LU, without success.
"As well as insulting our intelligence by the bizarre claim that Boxing Day is nothing special, London Underground has unilaterally torn up existing agreements," said the Aslef official.
"It used to be almost guaranteed that if you worked one bank holiday, you would not work the next. But the increase in service levels has meant this is now no longer possible.
"We are not opposed to additional services for customers, but we believe that there are times when staff need to be appropriately compensated for working at highly unsocial times - and that includes Boxing Day.
"If they get away with this, next year they'll be telling us Christmas Day is a normal day as well."
The Rail Maritime and Transport union and Transport Salaried Staffs Association have held a series of strikes in recent weeks in a separate row over job losses and are planning another 24-hour walkout at the end of the month.
Talks are being held at the conciliation service Acas but there is little sign of a breakthrough to the deadlocked row.
There were delays again on the Tube this morning when the District Line was part suspended and there were problems on the Victoria Line because of a defective train.
A Transport for London spokesman said: "London Underground has a long-standing agreement with all of its trade unions which cover staff working arrangements on bank holidays, and Boxing Day is included in that agreement.
"LU has made every effort to resolve this issue with the Aslef leadership, which has refused to attend talks at Acas to discuss its claim for triple time and a day in lieu for its members."
A TfL spokesman said: "A signal failure on the westbound District Line at Cannon Street at 8am caused severe delays - up to 30 minutes - on the line this morning with services affected back to Barking.
"The Circle Line, which shares tracks with the District Line at this point, is suspended in a clockwise direction. An engineer is now on site."