The union is urging its members to reject a new offer, which will be put to a ballot.
Further rail strikes are scheduled over Christmas, with the RMT union confirming planned industrial action will still go ahead.
It will be instructing its members not to work from 18:00 on 24 December until 06:00 on 27 December.
The action is being taken over a long-running dispute over pay, jobs and conditions.
Strike action set to begin next week, with dates in December and January, will go ahead as planned, the RMT said.
Industrial action will be held across four 48-hour periods on 13-14 and 16-17 December, and 3-4 and 6-7 January.
Mick Lynch, general secretary of the RMT union, said that said no improved offer on pay and working conditions came from the Rail Delivery Group on Monday as the ongoing row continues.
The union on Monday put a new offer from Network Rail to its members in an electronic referendum which will close next Monday, with a recommendation from the union to its workers to reject that offer.