Carriages will be cut during peak time services in order to make trains available for driver training, says London Midland.
Following a recruitment campaign, the train company is now training 61 new train drivers leaving some services between Milton Keynes and London with fewer carriages this month.
London Midland has been criticised in the past for running services with less than the required number of carriages at Leighton Buzzard train station, leaving commuters unable to get on the train.
A spokesman for the operating company, which runs services on the West Coast Main Line from London Euston, says London Midland has tried to ensure that no more than two peak time trains in each direction will be affected.
Tom Joyner, operations director of London Midland, said: “Our new drivers need to learn about the trains they will be responsible for. To do this we have chosen the quietest time of the year to take some carriages out of service.
“While it does mean, regrettably, some passengers may find it harder to find a seat on some busy trains this month all passengers will benefit from us having extra drivers available later this year.”
Here is a list of the train services that will be affected on weekdays until August 23:
Towards London Euston
0554 Milton Keynes Euston
0648 Milton Keynes to Euston
0804 Tring to Euston
0901 Tring to Euston
0956 Tring to Euston
1247 Milton Keynes to Euston
1655 Tring to Euston
1747 Milton Keynes to Euston
From London Euston
0704 Euston to Tring
0805 Euston to Tring
0904 Euston to Tring
1124 Euston to Milton Keynes
1624 Euston to Milton Keynes
1634 Euston to Tring
1821 Euston to Milton Keynes
1852 Euston to Milton Keynes