The indefinite reduction of around 694 weekday services is needed so ScotRail can provide a reliable service, chief executive officer Joanne Macguire told a meeting of passenger watchdog Transport Focus in Edinburgh.
The new “temporary timetable” confirms The Scotsman revealing the planned cut on Monday after 100 or more services a day were halted over the past week because of a “significant” number of drivers not working overtime after rejecting a 2.2 per cent pay offer.
Drivers’ union Aslef has now ordered a strike ballot.
ScotRail said it was also preparing reduced timetables for Saturdays and Sundays, with similar reductions to 67 per cent of normal services.
The news comes just days after ScotRail increased weekday services from 2,000 to 2,150, which will now be slashed to 1,456.
They include Edinburgh-Tweedbank services reduced to hourly and Glasgow-Aberdeen to two-hourly.
Ms Macguire said: “We plan to reduce our timetable to around 70 per cent.”
She said wanted passengers to be confident their train would turn up.
Ms Macguire said: "Due to the … withdrawal of rest day working by some colleagues, we have no option but to move to the reduced timetable and to be confident that we can deliver it well.”
However, she denied ScotRail was being ruthless by cutting more services beyond current disruption levels, which have reduced services by up to around 20 per cent.
Ms Macguire said: “We are not playing hardball with the unions, because ultimately those who suffer are our employees, and that is not our intention.
"We are not in any way trying to be disruptive or punitive towards our staff.”
She said she would not be confident of being able to run more services because of lack of staff.
Chris Gibb, chief executive of Scottish Rail Holdings, which oversees the newly-nationalised ScotRail for the Scottish Government, said ScotRail would have “more than enough” drivers undergoing training to be able to run its full current timetable without rest day working in due course, but it had been delayed by Covid restrictions.
He told the meeting: "As drivers become competent, we will reinstate services as necessary in the coming weeks and months.”
However, he was unable to say when the timetable would be restored.
On the pay dispute, Mr Gibb acknowledged ScotRail staff were “not immune from the cost-of-living crisis”.
"We are in territory around that a whole generation of people have not experienced.
"I hear the voice of the union representatives loud and clear, that they want to see an inflation-related pay increase.”
But Mr Gibb warned: “The railway in Scotland is now in direct competition for public funding with schools and hospitals.”
Aslef Scottish organiser Kevin Lindsay said: “This is what happens when you have political interference in industrial relations.
"It’s time the Scottish Government allowed ScotRail and Aslef negotiate in a fair and open manner.
“These cuts will have a devastating effect on passengers and their confidence in our railway.
"It’s industrial vandalism by the Scottish Government.”
Scottish Conservatives transport spokesperson Graham Simpson said: “This is devastating news for passengers.
"We are only weeks into having the SNP running our trains and already it is chaos.”
It comes as a total of 225 ScotRail services were cancelled or amended by driver shortage on Wednesday.