Trains could grind to a halt after a union launched a strike ballot of its members at Northern Rail.
The Rail, Maritime and Transport (RMT) union will ballot more than 2,000 members at the company in a dispute over casualisation of the workforce, pay and working conditions.
Trains through Wakefield Westgate and Kirkgate could be hit by industrial action after ballot papers are sent out next week to all the RMT members including drivers, guards and managers.
The RMT is protesting against the use of agency and sub-contracted workers who it says should instead by directly employed by Northern Rail.
The union claims this breaches working agreements and leaves casual staff with worse pay and pension provisions than Northern Rail employees.
RMT General Secretary Bob Crow said: “There is a cynical drive to use casual, agency staff to undermine job security, pay and working conditions on Northern Rail and our members are furious that not only have the company refused to stop this practice but they are driving it forwards.
“RMT has made it crystal clear that casualisation and a breach of our agreements are an outright attack on all of us and will not be accepted in any way, shape or form.”
Mr Crow added: “RMT remains available for meaningful talks.”
A Northern Rail spokeswoman said the company was disappointed about the ballot and would work with RMT representatives to try and resolve the dispute.
The ballot will close on May 20.