Swimming groups are planning peaceful demonstrations outside the two meetings which will see the future of the Hampstead Heath bathing ponds decided.
Pond-users are up in arms about the City of London Corporation's (CoLC) plans to more than double the price of day tickets to swim on the Heath and make payment compulsory.
The CoLC has defended the proposed move and said it must make changes in order to make sure swimming at the ponds is sustainable.
In a report prepared for a meeting of the Hampstead Heath Consultative Committee on March 9 and the Heath Management Committee on March 11 - when a final decision will be made - CoLC officials set out recommendations for change which would see prices increase to £2.40 for concessions and £4 for adults.
Under the preferred option, the CoLC's subsidy to swimming on the Heath would fall from £994,000 to £443,000 a year.
Heath bosses plan to freeze season ticket prices for concessions and offer free swimming to the under-16s and over-60s before 9.30am.
Swimmers said it had been a "sham" consultation and said an "overwhelming majority" opposed compulsory charging.
Karina Dostalova, who chairs the CoLC's Heath management committee emphasised as yet no decision had been made.
She said: "We are proposing a new support fund for people who cannot pay to swim, and we are freezing season ticket prices, so the ponds remain fully inclusive."
She said Heath bosses were considering introducing contactless payments and employing a ranger "to welcome swimmers" but had no plans to bring in turnstiles.
The CoLC's rationale has been questioned by the swimming groups - who feel earlier this year they were presented with a fait accompli, rather than a meaningful consultation
They have complained to Heath bosses have not done enough to encourage voluntary donations.
According to Professor David Gilbert, a swimmer at the men's pond, the new charging levels could make the CoLC up to £740,000.
Chris Piesold, chair of the Highgate Men's Pond Association said: 'We are angry.
"This consultation has been rushed through in just seven weeks, we came to it in good faith, but it now seems that the result was a foregone conclusion."
Nicky Mayhew, co-chair of the Kenwood Ladies' Pond Association agreed, saying the CoLC "don't seem to understand what makes these ponds unique".
The swimmers have also called into question whether the CoLC will be able to implement a new system within its two-month timescale.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here