The ScotRail dispute threatens to escalate with drivers’ union Aslef warning that it could be drawn into the row over who controls train doors.
Union leaders will next week seek assurances that ScotRail will not introduce more driver-controlled trains.
Scotland district secretary Kevin Lindsay said such a move “may lead us into some sort of conflict”.
He declined to say whether that could include a strike ballot, but said next Thursday – the day of the meeting – would be “quite a defining day”.
Pressure for action has already come from the union’s Edinburgh branch, which voted on Sunday to demand a ballot if ScotRail did not provide “satisfactory answers”.
There have also been reports of drivers planning to take unofficial action by not working overtime, which could force train cancellations.
The RMT union has already staged ten days of strikes against plans for drivers to take over door control from conductors, or guards. Further walkouts have been called for the next two Sundays.
Aslef is on a potential collision course with ScotRail because the union’s agreed policy is to oppose further driver-controlled trains.
The operator is due to introduce new trains on lines across the Central Belt from next year, including the main Edinburgh-Glasgow route.
ScotRail has withdrawn plans sent to conductors for drivers to control the doors on this fleet, but the unions believe its intention is clear.
Transport Scotland also confirmed yesterday the planned reduction in journey time between the two cities from 50 to 42 minutes after electrification of the main line is complete is based on driver operation of the doors.
ScotRail has said drivers rather than conductors closing doors could save 15 seconds per stop. That could add up to more than a minute over the journey.
Mr Lindsay said that following next Thursday’s meeting “we will evaluate what we are going to do next. It’s too early to say what”.
ScotRail said the meeting was to discuss the Strathclyde Manning Agreement – a deal struck 30 years ago for driver operation of doors on many trains in and around Glasgow.
It said: “We won’t be tabling any proposal on an extension of driver-only operation.
“If we get to a point with the RMT where we may have a proposal emerging, then we would want to discuss that with Aslef also. However, at the moment, there is nothing to discuss.”