Islwyn MP Chris Evans has written to Arriva Trains Wales to ask what the company is doing to protect passengers from increasing prices.
Mr Evans said some rail users have seen the cost of their ticket rise by as much as 10% as prices increase above inflation for the tenth consecutive year.
He said: “As workers return to work after the New Year, those who commute by train will have found that they now have to fork out even more for the cost of their ticket.
“It seems to me that under this government more and more people are being priced out of their commute – with drivers facing rising fuel prices, funding for bus services being axed and the cost of train tickets spiralling out of control.
“That is why I have written to the Chief Executive of Arriva Trains Wales as I am increasingly concerned that extortionate rail fares will cause many workers to decide they simply cannot afford to get to work.”
Last month, Caerphilly AM Jeff Cuthbert also wrote to Arriva Trains Wales asking for a price freeze.