ScotRail will cut almost 700 services a day from Monday, due to a shortage of drivers in an ongoing pay dispute.
Evening trains on many routes across Scotland will terminate hours earlier.
It comes just a week after the operator, which was nationalised last month, launched a new timetable.
Hundreds of trains have been cancelled since 8 May when many drivers opted not to work overtime. Drivers' union Aslef had balloted members for strike action after rejecting a 2.2% pay offer.
The May 2022 timetable had approximately 2,150 weekday services. From next week this will be reduced by a third to 1,456.
Similar cuts are expected to be made to the Saturday and Sunday timetables with details expected to be made public in the coming days.
David Simpson, ScotRail service delivery director, said: "We are very sorry to customers for the disruption of recent days.
"We know what customers want more than anything is certainty and reliability, which is why we are introducing a temporary timetable.
"We want to resolve this dispute with the trade unions and move forward together to provide the safest, greenest, and most reliable railway we can for Scotland."
Mr Simpson said the company remained open to further talks with the unions. He urged customers to check their journey times.
Evening travel has been affected on many routes, with last trains departing hours earlier.
Edinburgh to North Berwick currently departs at 23:14. From Monday the last train will be at 19:40.
The last train from Glasgow to Stirling is currently 23:51. From Monday it will be at 19:49.
The Aslef union accused the Scottish government of "industrial vandalism" over the cuts.
Kevin Lindsay, Aslef Scotland organiser, said: "This is what happens when you have political interference in industrial relations.
"It's time the Scottish government allowed ScotRail and Aslef to negotiate in a fair and open manner.
"These cuts will have a devastating effect on passengers and their confidence in our railway."
ScotRail has been run by a company owned by the Scottish government since 1 April.
The previous operator Abellio had its franchise ended early amid criticism of the quality of the service.
Opposition parties also condemned the service cuts.
Scottish Conservative transport spokesman, Graham Simpson, said: "It is damning, but not surprising, that the first thing the SNP do with the newly nationalised ScotRail is slash almost one third of services.
Scottish Labour's transport spokesman, Neil Bibby, said: "Services are being plunged into chaos, workers are being treated with contempt, and passengers are being left in the lurch. The SNP must take responsibility for fixing this mess."
Scottish Liberal Democrat transport spokeswoman, Jill Reilly, said it was an "ill omen" for the newly nationalised service.
She added: "Scotland should be encouraging people onto the most environmentally friendly form of mass transportation. You don't do that by making rail travel less convenient for users.
The new timetable comes after significant number of drivers declined to make themselves available for overtime or Sunday working during a pay dispute.
The Aslef union rejected a 2.2% pay rise and balloted drivers over strike action.
ScotRail had been relying on drivers working extra hours, following delays in training new staff during the Covid pandemic.
On Monday, Mick Hogg of the RMT union, described the situation as an "absolute shambles".
He said he had recommended that the RMT ballot members for action short of a strike, with any action co-ordinated with Aslef.
Scotland's transport minister, Jenny Gilruth, described the practice of rest day working as "outdated" and said the Scottish government was looking to phase it out.
She said the delayed driver training was expected to take a few months.
BBC Scotland has approached Transport Scotland for comment.