A system that charges charities for holding fundraising challenges on Ben Nevis might be illegal, according to a report.
The Glen Nevis Visitor Centre in Fort William, run by the Highland Council, asks charity event organisers to book two years in advance and pay a fee to cover litter collection and toilet cleaning.
The fee is up to £250 for groups of under 50 and a minimum of £250 for groups of more than 50.
Charities have been warned by the centre that if they twice fail to book events they will be no longer welcome to use the facilities.
But a report by access rights campaigner Andy Strangeway says that a compulsory booking and fee-charging system for climbing Ben Nevis is illegal, breaching the Land Reform (Scotland) Act 2003.
"Under the act, no one, be it an individual, group or charity, has to book in advance to exercise their access rights responsibly across Scotland," said Strangeway. "All have a legal right of free access."
Strangeway's report says Highland Council should clearly state that the charge is not to book an event on Ben Nevis and the council should charge everyone or no one at all.
A spokesman for Highland Council said that charging event organisers for additional services, which has been in place since 2006, did not constitute wilful restriction of access to Ben Nevis and was not illegal.
Additional services were required to deal with the impact of large numbers of people using the site in a short period of time, he said.
The report also says the Institute of Fundraising should tell members that the charge might have no legal basis.
Louise Richards, director of policy and campaigns at the institute, said: "The institute is against anything that constitutes a charge on fundraising and which results in a lower percentage of donations going to a cause."