A staff ballot by the Rail, Maritime and Transport union (RMT) will start on Friday after its national executive agreed with Scottish officials that members should be recommended to vote against the revised 5 per cent offer because of a clause over the use of new technology.
The three-week vote by 2,886 members who account for more than half the ScotRail workforce will be completed on August 4, but a further ballot would be required for any strike action.
The move came on Thursday hours after drivers union Aslef announced a strike on Saturday July 30 at cross-Border operator LNER and other English-based train operators in a separate pay dispute.
On Wednesday, the RMT also called a fourth Britain-wide strike on Wednesday July 27 in its dispute with Network Rail and English-based train operators, with the previous three in June halting most ScotRail services.
In the ScotRail dispute, RMT Scottish organiser said: "The referendum opens tomorrow [Friday] and closes on August 4 with a recommendation to reject based on introduction of technology without an agreement.
"The RMT is a member-driven union where the members will have the final say.
"The RMT negotiating team have gone as far as we could with ScotRail management and this is the best offer that could be negotiated.
"In the circumstances, it is only right and democratic that RMT members have their say on this offer."
The decision came despite members of drivers’ union accepting the deal in a vote on Monday.
ScotRail said last month it was confident RMT members would support its “strong offer”.
Head of customer operations Phil Campbell said on Thursday: “We’ve made a really good offer which recognises the cost-of-living challenges faced by families across the country and delivers good value for the public.
“The feedback we’ve had from many colleagues across our general grades is that they recognise we have made a series of very good offers and we are pleased they will get a say in a referendum.
"We would urge them to support acceptance of the offer.”