An estimated 2,000 rail passengers refused to pay fares on Monday in protest at the state of services, a campaign group claims.
Passengers were asked to hand in fake tickets
Early morning commuters travelling between Bath and Bristol say they are fed-up with late and crowded trains.
Protest group More Trains Less Strain urged passengers to hand in fake tickets rather than pay for real ones.
But First Great Western spokeswoman Elaine Wilde said many protesters took fake tickets but still paid their fare.
"We do not know of anyone who has refused to buy a ticket this morning," she said.
"People are taking the leaflets and fake tickets but are not using them.
"Only one person has done so and that person was allowed to travel."
The campaign group says timetable changes have caused chaos, and a lack of carriages has left them standing in dangerously cramped conditions.
The protest took place during the rush-hour when commuters were urged to present a "fare strike" ticket designed and handed out by the group.
The strike tickets were intended for use by anyone travelling from two stations in Bath to Bristol, Keynsham or other destinations in the South West.
More Trains Less Strain spokesman Tony Ambrose estimated that more than 2,000 passengers took part in the protest.
He said: "The turnout has exceeded our estimations.
"This has sent out a really strong message to First that commuters just can't be taken for granted any more.
"Things have to change, they simply cannot go on as they are at present."
Bath Liberal Democrat MP Don Foster added: "I can't condone people breaking the law and not paying for their tickets, but the protesters are right, we're getting a dreadful service from First Great Western."
Charity worker Mr Ambrose said problems had begun in December when the number of carriages and frequency of trains was reduced.
First Great Western (FGW) said the problems had been caused by a backlog of maintenance work which the company was working hard to clear.
Regional manager Andrew Griffiths said: "We do understand why people have been upset.
"We have had these maintenance difficulties, but our new £8m depot in Bristol has pretty much caught up with the backlog."
On Monday, passengers were reported to be showing the fake tickets to guards and being waved through gates.
Customers were warned that travelling without a valid ticket risked prosecution, the maximum sentence being a fine of £1,000 or three months imprisonment.