Avanti is to run a reduced service between London to Manchester on Saturdays until the end of the year.
Train operator Avanti West Coast will be cancelling nearly 20 services every Saturday between London Euston and Manchester Piccadilly until the end of the year.
It had earlier announced plans to scrap two in five of the trains it runs on the popular route from December 9.
However the BBC understands the reduced timetable will start immediately.
First reported by the Sunday Times newspaper, Avanti blamed a shortage of train crew and industrial disputes.
Avanti West Coast is joint owned by First Group and Trenitalia. It typically runs around 50 services – roughly three an hour at the busiest times – between London and Manchester every weekday.
A similar number of services also run on Saturdays, but from next week that is being reduced to just 30 trains.
Avanti said it is working hard to minimise disruption.
Train operators must keep cancellations below a certain level to fulfil their contracts, and a failure to do so could lead to them being fined and possibly stripped of the contract.
But if ministers agree to temporarily reduced services – known as “short-term planning arrangements”, the cancellations do not appear in official statistics.
Avanti did not confirm it has sought such an arrangement, but the Department for Transport confirmed that planned timetable reductions until 1 January 2024 were agreed “in accordance with the requirements set out in Avanti’s contract”.
A spokesperson added: “Despite progress since last year, Avanti still needs to further improve and we continue to hold it to account for matters within its control.
“Traincrew shortages, linked to train drivers on average £60,000 salaries refusing to work overtime, highlight the need for modernisation across the wider railway that is being resisted by unions.
“The temporary timetable changes were necessary to minimise short-notice cancellations due to traincrew shortages and to accommodate engineering works that will maintain and improve the resilience of the network.”
An Avanti West Coast spokesperson said: “We have been seeing some short-notice cancellations on our network and would like to apologise to our customers for the inconvenience caused.
“We know this is not good enough and are working hard to make sure we can minimise these cancellations.”
But Aslef, the union which represents train drivers, was scathing about the changes.
Mick Whelan, its general secretary, said: “Avanti West Coast is yet again letting passengers, and the taxpayer down. The problem is the company does not employ enough drivers to deliver the services it is contracted, and has promised, to run.
“Avanti West Coast needs to do the right thing, by staff, by passengers, and by the taxpayer.”