A potential rail strike could cause disruptions for South Yorkshire rail passengers over the busy festive season.
The Rail, Maritime and Transport union is balloting its members for both strike action and action short of a strike who work on the Virgin East Coast services - many which connect Sheffield and Doncaster to other parts of the country.
The union claimed inferior conditions were being imposed on staff as well as changes to working conditions and sick pay.
Voting papers will be sent out on Friday and the ballot will close on December 20.
RMT general secretary Mick Cash said: "We will not stand by while Virgin East Coast attempt to impose a two-tier workforce with different terms and conditions for our members.
"Virgin East Coast are also seeking to unilaterally enforce changes to working and conditions, including sick pay arrangements, which would have a major impact on our members' working lives.
"The pay offer was put to our members and they rejected it by a large majority."
In a separate dispute over pay, members of the RMT and the Transport Salaried Staffs Association on Virgin Trains West Coast are to stage a series of strikes in December and January.
A Virgin Trains spokesman said: "We have offered members what we believe is a very fair 3.2 per cent pay increase and we remain open to discussions with them."