Eight illegal workers have been detained following a pre-dawn immigration raid on a house in Perth.

Eight Malay nationals, suspected of working illegally in nearby market gardens, were held after a tip-off.

The men are now in immigration detention while arrangements are made for their removal from Australia.

A Department and Immigration and Citizenship spokesman warned employers who hired illegal workers - whether they knew it or not - were now liable to fines and other sanctions under new rules that came into effect on June 1.

Penalties range from $3060 to $76,500 per illegal employee.

"People who arrange work for others who have no right to work also face severe sanctions," the spokesman said.