The nurses' union says members would accept a 15 per cent pay rise over three years after a work ban commenced at Royal Perth Hospital.

The union began campaigning for a 20 per cent pay rise last year.

That would have boosted the average annual salary from $73,000 to $87,000.

Nurses at RPH stopped performing non-nursing duties this afternoon, including re-stocking, cleaning, and moving patients.

Similar bans are set to commence at Fremantle and Sir Charles Gairdner hospitals this week.

The state secretary of the Australian Nursing Federation, Mark Olson, says he expects beds to be closed in a couple of weeks unless the State Government agrees to the union's pay claim.

"The nurses tell me that they'd be satisfied with 15 per cent over three years because that would just take them to the top of the table," he said.