Mr Schwarzenegger has denied any conflict of interest

American Media Operations said the former actor, who is governor of California, was receiving 1% of the company's advertising revenue.

Critics say the deal could amount to a conflict of interest.

The governor's spokeswoman denied any conflict, saying he had complied with laws on revealing income.

Mr Schwarzenegger, who was elected in 2003, has rejected his $175,000-a-year salary as governor.

But California law allows governors and other elected officials to keep outside jobs.

Dietary supplements

American Media Operations, a subsidiary of American Media Inc. which publishes Flex and Muscle & Fitness magazines, revealed the payments in documents filed with the US Securities and Exchange Commission.

This is one of the most egregious apparent conflicts of interest that I have seen Larry Noble Political observer

The payments, confirmed by the governor's office, could be as high as $8m over five years.

The magazines receive much of their advertising revenue from companies producing dietary supplements.

Last year, Mr Schwarzenegger vetoed a bill that would have introduced state regulation in the supplement industry.

Jackie Speier, a Democrat in the California State Senate and the bill's sponsor, said the governor should quit the company.

"Whether it is an actual conflict or not, it certainly gives the appearance of being a conflict," she told the Associated Press news agency.

Judgment questioned

Larry Noble, who heads the Center for Responsive Politics, a Washington watchdog, said he thought there was a clear conflict.

"This is one of the most egregious apparent conflicts of interest that I have seen," he said.

"This calls into question his judgment as to who he is working for, and it calls into question what he thinks he owes the public."

But Margita Thompson, a spokeswoman for the governor, said that while his financial affairs were "probably the most complicated of any governor", he had kept within the law.

"The governor did not direct sales or marketing activities of American Media and did not have personal contact with any advertisers to generate the advertising revenue," she said.

Mr Scharzenegger's contract with American Media calls on him to help the company with suggestions about "overall editorial direction". He is not required to work there during normal business hours.

The governor also writes monthly columns for both magazines.