Passengers travelling between London and Shropshire will be charged higher train fares from September.
Wrexham and Shropshire is the only firm offering direct Shrewsbury to London train services and has not raised its prices since it started in 2008.
Fares will rise by up to £10 to reflect growing customer demand and the fact the firm is running at a loss, it said.
A passenger watchdog said customers had rated the service very highly in the past but might not like the price rise.
Passenger Focus said: "It will be interesting to see how passengers react to a sharp price hike and whether they will find the service as attractive if prices are set at this level."
The firm had previously been given 99% in a Passenger Focus customer satisfation survey published in June.
Wrexham and Shropshire's managing director Andy Hamilton said: "We are trying to encourage people to travel on the quieter trains if they are able to, but to leave the busier trains for people who need to travel at those times of day."
Fares on the 0552 Shrewsbury to London Marylebone and 1630 return service are due to rise from £40 to a maximum of £50 for flexible date travel tickets.
Weekend services will remain the same and advance fares are available on all trains.
The firm had a 25% increase in passengers in the past 12 months but has not made a profit.
Mr Hamilton said he needed more customers, which is why he had not increased fares for most services but fuel costs had risen.
- 22 June 2010