Avanti West Coast said it is cancelling Saturday services at short notice due to staff shortages.
This comes after it reached an agreement with the Department for Transport (DfT) earlier this month to reduce its Saturday timetables between London and each of Birmingham, Manchester and North Wales from December 9 until the end of the year.
The frequency of trains between London and Manchester will reportedly be cut from three per hour to two per hour.
Services removed from timetables in advance are not classified as cancellations, meaning they do not impact performance statistics.
An Avanti West Coast spokesman said: “We have been seeing some short-notice cancellations on Saturdays 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.
“These service changes are a result of resourcing challenges where we have seen a shortage of train crew due to historic leave agreements and ongoing industrial disputes.”
A DfT spokesman said: “Despite progress since last year, Avanti still needs to further improve, and we continue to hold it to account for matters within its control.
“Train crew 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 train crew shortages and to accommodate engineering works that will maintain and improve the resilience of the network.”