ScotRail has urged TRNSMT festival goers to check their travel ahead of time due to its “significantly reduced service”.
The rail operator introduced a temporary timetable earlier this week in a bid to avert disruption after days of short-notice cancellations.
It cut about 600 services to preserve “certainty and reliability” after four unions rejected a pay offer last week.
ScotRail communications director David Ross told BBC Scotland that the temporary timetable would be in place “for the next few weeks at the very least”.
Kevin Lindsay, Scotland organiser for Aslef, previously warned that train drivers were likely to launch industrial action due to the “derisory” pay offer from ScotRail.
ScotRail said it was “fully committed” to further talks with the unions.
TRNSMT, Scotland’s largest music festival, is expected to attract about 50,000 people to Glasgow Green each day of the weekend.
It got under way on Friday with Liam Gallagher headlining the Main Stage, with performances from the likes of the Sugababes, the Last Dinner Party and Example throughout the day.
Gerry Cinnamon and Calvin Harris will headline on Saturday and Sunday respectively.
The festival starts at midday before closing late at night each day.
Mr Ross told BBC Scotland News: “We do have fewer late-night services than we usually would for TRNSMT so check before you travel and maybe consider alternative means of travel.”
Mr Ross added: “We’ve got a reduced service across our entire network and we’re operating around 50% of our normal Sunday timetable.
“Drivers are not making themselves available to work rest days, as is their contractual right.”
ScotRail said about 1,660 trains would operate between Mondays and Saturdays under the provisional measures.
It warned that peak-time services in the morning and late afternoon would have their frequency halved, from four trains per hour to two.
They include routes between Edinburgh and Glasgow, while those heading north of the central belt will also be vastly reduced.
Mr Ross said the temporary timetable was under constant review, adding: “Where we can add in additional service, we’re doing so.
“For example we’ve got a big special event like the Open coming up next week where we’ll have extra services and extra carriages for people.
“We are looking to get time in the diary with our unions over the course of the next few weeks because everyone wants to get this resolved so we can remove this temporary timetable, and we’ll hopefully make some progress in the next few weeks.”
ScotRail was embroiled in a long-running dispute with unions in the summer of 2022.
It resulted in hundreds of services being cancelled and the rail network grinding to a halt in large parts of the country.
The publicly-owned firm said it was attempting to recruit 160 new train drivers in order to improve reliability.