A Gloucestershire MP wants the government to sack First Great Western (FGW) and move the firm's train into the public sector.
David Drew, MP for Stroud, has tabled a Commons motion condemning the company, accusing it of "poor levels of punctuality, cuts in services and severe overcrowding".
A spokesman for FGW said punctuality was improving and although 11 trains were due to go "off lease" there would be "no cuts to services".
"Our most recent Public Performance Measure is 85.6%, compared to a low of 67% just over a year ago," said the spokesman.
The Labour MP is also concerned at reports "a dozen extra trains recently introduced by the company will be withdrawn at the end of the year", and claims it will mean there will have been a 20% cut in services since it took over the franchise a year ago.
Responding to that the FGW spokesman continued: "We cannot 'cut services' as we have a Service Level Commitment agreed with the government when we were awarded the franchise.
"We need 51 trains to run services in the former Wessex area and we have 71 trains to do this. There is nothing unusual about this as rolling stock is reshuffled all the time and it certainly won't mean a cut in services."
But the Labour MP said the company was not putting the "interests of passengers before the interests of shareholders", and is supporting calls by passenger groups and rail unions for the firm to lose its franchise.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article