A fitness company operating in five states is being investigated over allegations of illegal deductions from clients' credit cards.

Access Boot Camp has advertised its classes in Sydney, Brisbane, Melbourne, Perth and Adelaide.

New South Wales Fair Trading has launched an investigation after receiving several complaints from people who say the company has taken money without authority.

Fair Trading Commissioner Rod Stowe says the company has now stopped trading.

"The investigation that we'll undertake, what will be critical to that is seeking refunds for consumers who have not received the services that they've paid for," Mr Stowe said.

"We'll also be seeking to ascertain whether there were representations made by the business which were false or misleading and whether the business was in a position to supply the services that it had advertised."