More than 90 per cent of Victoria's paramedics say they would stop working night, weekend and public holiday shifts if penalty rates are cut, according to a new poll.

The results of the Reachtel survey of 1188 Victorian paramedics will be released at a health workers rally in the marginal seat of Dunkley on Saturday afternoon.

The poll, done on Wednesday, found that 92 per cent of the state's paramedics would no longer do shift work if penalty rates were cut.

Australian Council of Trade Unions, United Voice and Australian Nurses and Midwifery Federation members will gather at Frankston Hospital for a rally from midday.

The nurses and paramedics will protest against any threat to cut penalties.

ACTU secretary Dave Oliver said any moves to cut penalty rates would have a "disastrous impact" on the healthcare system.

Ambulance Employees Australia's Victorian general secretary said the Reachtel poll showed there was "no way" most paramedics would work nights, weekends and public holidays without penalty rates.

"Shift penalties make up an average of 27 per cent of a paramedic's weekly income," he said.

During the online debate earlier this month between Prime Minister Malcolm Turnbull and Labor leader Bill Shorten, Mr Turnbull said penalty rates would not be changed if the Liberals were voted in for a second term.

However, he also said any such changes were "a matter for the independent umpire", referring to the Fair Work Commission.

Dunkley is currently held by retiring Liberal MP Bruce Billson.