A train company is holding an investigation after a disabled man claimed he was not allowed to board a crowded carriage.
Colin Williams, from Welshpool, claimed a guard refused to let him board a train to Shrewsbury saying it was full.
But Mr Williams, 41, said several other passengers were allowed to the board the train, while the guard did not lower the ramp for his wheelchair.
Arriva Trains Wales said it was investigating the matter.
Mr Williams, who has cerebral palsy, and uses a wheelchair, was travelling alone to Shrewsbury to watch a friend perform at a music festival when he was left at Welshpool railway station on Saturday 5 April.
"I was one of about 20 passengers waiting to go on the train but the guard made no effort to get the ramp to get me on, even though people told him they would help me to the disabled area," said Mr Williams.
The ramp for disabled passengers is kept on the train, but the guard refused to lower it.
Mr Williams said: "I asked for the ramp to help me get on the train but the guard told me there was no room on the train for me.
"I told him I was willing to go anywhere on the train but he refused to let me on.
"I would have been quite happy to travel in the aisle with other people because the journey to Shrewsbury only takes about 20 minutes.
"As far as I am aware I was the only passenger that didn't get on that train.
"It was a humiliating experience and I felt discriminated against because of my condition.
"I have written a letter and an e-mail to Arriva Trains asking for an apology."
Mr Williams was able to board the next train which was two hours later.
"By the time I got to the event my friend had already finished his performance," said Mr Williams. "My day was ruined and I am upset at the way I was treated."
Mr Williams has since talked to passengers who were boarding and alighting the same train.
He said: "One person who got on that train has told me there was plenty of room if people had moved down the aisle a little bit."
A disability group has urged the train company to ensure its staff are made aware of its own policies regarding disabled people.
It said the 2010 Equality Act makes it unlawful for organisations which provide services to the public to discriminate against disabled people in the way they provide or do not provide those services.
Rhyan Berrigan, Disability Wales' Transport Policy Officer, said: "It is very poor customer service and it is clear the guard was not following procedures properly.
"We urge Arriva Trains Wales to ensure that all staff are made aware of their own policies and procedures regarding disabled people."
An Arriva Trains Wales spokesman said: "We are sorry to hear that the passenger was unable to board the Aberystwyth to Shrewsbury service at Welshpool station and we are currently investigating this matter.
"Arriva Trains Wales remains committed to reducing social exclusion through a positive policy of improved access to trains and stations and works closely with rail industry colleagues and stakeholders to achieve this through positive partnerships."