A furious row has broken out between unions and a rail operator that has slashed its train timetable and suspended ticket sales blaming "severe staff shortages".
Avanti West Coast is expected to run as few as four trains per hour from Sunday, with services from London the worst affected.
Usually it operates up to seven trains per hour on the West Coast Main Line.
In a letter to the rail industry, the company's managing director Phil Whittingham, said that the "current industrial relations climate" was resulting in "severe staff shortages in some grades through increased sickness levels, as well as unofficial strike action" by union members.
But unions hit back at the claims on Tuesday and demanded an urgent meeting with Transport Secretary Grant Shapps over the crisis.
Aslef insisted its members working at Avanti West Coast are not involved in any strike action before planned walkout on Saturday in a long-running dispute over pay and conditions.
In a letter to Mr Shapps, RMT general secretary Mick Lynch also denied unions were taking any unofficial action.
He said: "Avanti are falsely and shamefully making allegations that this decision is due to unofficial industrial action when the reality is this decision arises from poor management, cutting staffing to the bare minimum and rock bottom staff morale.
"I am presuming that you sanctioned this decision, and I would therefore be grateful for an urgent meeting to discuss the crisis."
From this weekend Avanti is expected to only run four trains an hour from London Euston to Glasgow, Liverpool, Manchester and Birmingham - one going to each city.
Previously the company was running three services an hour to Manchester.
The limited timetable will be in place "until further notice", Avanti West Coast said.
Mr Lynch said that the Government should clarify whether Avanti had permission to implement a reduced timetable and if it was now in breach of its contract with the Department of Transport.
He added: "The government cannot continue to take the side of corporations against passengers and workers, and I look forward to your agreement to an urgent meeting to discuss this crisis."
The Department for Transport said it would not be commenting on the dispute.
Avanti was contacted for further comment.