Cleaners, gardeners and school assistants in WA public schools have been told their pay will be cut if they continue with work bans.

School support staff began industrial action this week after the Government rejected their call for a 20 per cent pay increase.

It offered them 8 per cent over three years.

Dave Kelly from the Liquor, Hospitality and Miscellaneous Union says members are not getting fair treatment from the government.

"The government's decision to threaten them with having their pay stopped is really unprecedented," he said.

"The government has obviously decided to take a heavy-handed approach with cleaners and educational assistants."

But Cliff Gillam from the Education Department says staff members have a duty of care to the students to continue performing their jobs.

"The action has been bans on such things as emptying bins and not raking sandpits, which can lead of course to there being hazardous items that are not revealed and that creates a danger," he said.

"So fairly minor actions, but actions that none the less do have the capacity to affect the safety and the health of the school environment."