The cost of swimming is set to treble for many pensioners in Hounslow as annual passes are phased out across the borough.
Senior citizens currently pay around £100 a year for unlimited use of the borough's public swimming pools and saunas.
But Fusion, which runs leisure centres on behalf of Hounslow Council , is ending the swim-only memberships.
Anyone wishing to enjoy unlimited swimming must now sign up for a full gym membership, which getwestlondon has been told costs around £37 a month, or £300 for the whole year.
Visitors can still pay £4.80 a pop to swim at any public pool, or £2.85 for concessions, which would work out cheaper than a full membership for OAPs taking the plunge less than twice a week.
A council spokesperson said customers paying monthly by direct debit had been advised swim-only memberships would cease in three months' time, and those with annual passes had been told they would be honoured until the end of their term.
Harkrishan Saini, of St Paul's Close, Hounslow, is one of the card holders affected. He claims neither he nor any of his friends were notified of the changes and says many pensioners will struggle to afford a full membership.
"I don't know anybody who received a letter about what was happening," said the 77-year-old former civil servant.
"It came as a big shock to us when we were told our cards were not valid at the new Heston leisure centre.
'Swimmers not notified'
"Several years ago Fusion said it was getting rid of the swim-only passes but Ann Keen, who was our MP at the time, successfully campaigned to keep them.
"The full gym passes are much more expensive and I think this will put many older people off swimming, which could cost more in the long-run if their health is affected."
The new arrangement only came to light after Heston Fitness and Leisure opened in January and angry customers were told their swim-only passes were no longer accepted there.
The council says letters were sent in December 2013, when the old Heston Pool leisure centre closed, and again in 2015 to inform swim-only members this would be the case.
But more than half a dozen people have now contacted getwestlondon claiming they were never notified, and the council has failed to respond to our request for a copy of these letters.
The council said it appreciated swim-only members may not have been reminded of this at the time of renewal.
Because of this, it said Fusion had issued complimentary two-week full access passes to all those affected for use at Heston Fitness and Leisure.
getwestlondon understands the swim-only passes are not available at leisure centres run by Fusion in other boroughs.
Campaigners say they have collected more than 500 signatures on a petition calling for the swimming passes to be retained.
They have given it to Councillor Rajinder Bath, who is due to present it at the borough council meeting on Tuesday, February 23.