The Malaysian government says it plans to expel more than a million illegal migrant workers.
By Jonathan Kent
BBC correspondent in Kuala Lumpur
The country's Home Minister says 400,000 members of Malaysia's volunteer corps will be mobilised and special squads are already being trained to enforce their removal.
No official reason has been given, but there is widespread concern in Malaysia about rising levels of crime.
The government estimates that there are around 2.5 million foreign workers in Malaysia, forming around 10% of the population, and that half of them are here illegally.
Home Minister Azmi Khalid warned the businesses that employ the illegal immigrants not to complain when their workers are rounded up. "We are serious," he said.
Two years ago the government carried out a similar operation. There were huge crowds at ports and airports as hundreds of thousands of migrants, mostly from Indonesia, the Philippines and the Indian sub-continent, tried to beat the deadline to leave.
But building sites in Kuala Lumpur and around the country came to a standstill and restaurants cut back their menus as workers headed home. However, when the operation to remove them had run its course, the workers drifted back.
Then, the government said it had taken action because illegal immigrants were responsible for an increase in crime.
Fear of crime
With the Malaysian papers full of reports of violent robberies allegedly involving foreigners, crime may again have prompted the authorities to take a tough line.
However, the minister didn't spell out exactly when the round-up would take place.
He said illegal workers would be thrown out before Malaysia completes the introduction of its new microchip identity card, but no-one seems to know when that will be.