Railcard train fare discounts are being cut by operators this month.
Savings are advertised as being one-third and are currently applied at a rate of 34% for railcards held by people including those aged 16-30 and over 60.
The discount will be trimmed to 33.4% from the middle of September as operators take advantage of an “easing of system limitations”.
While the move will add only small amounts to individual ticket prices, a pro-rail group has described it as a “step in the wrong direction”.
The cut will take effect from 15 September, the PA news agency understands.
An off-peak return from London to Manchester, which costs £109 at full price, is available for £72.55 on Sunday 15 September for railcard users.
The same ticket on Saturday 14 September is reduced to £71.90.
Other railcards affected include those for families travelling with children, people with a disability and military veterans.
Other examples of anytime return fare increases for railcard holders include from £194.15 to £195.90 for Cardiff to London, and from £72.60 to £73.25 for Birmingham to Manchester.
A section on railcard discounts on the National Rail Enquiries website was updated in June to remove references to 34%.
Bruce Williamson, of lobby group Railfuture, said: “While this represents a very tiny increase in fares for some passengers, it’s a step in the wrong direction.
“As the slogan goes, every little helps, so why risk irritating passengers for a few pence?”
Michael Solomon Williams, of pressure group Campaign for Better Transport, called for the introduction of a northern network railcard to make the system “fairer” by giving passengers in the north of England “the same discount offered to many of their southern counterparts by regional railcards”.
A spokesperson for Railcard, the organisation which manages the discount cards on behalf of train operators, said: “The cost of a Railcard hasn’t increased for over 10 years and will continue to provide customers with a third off their rail fare for just £30 a year – a cost that can be made back in just one or two journeys.”
The rail industry is striving to boost fares income, which remains lower than pre-coronavirus levels.
Office of Rail and Road figures show revenue from passengers was £10.3bn in the year to the end of March, compared with £12.7bn 2019-20.