The large-scale operation, codenamed Ops Tegas, is to round up and deport illegal immigrants, mainly Indonesians, from Tuesday.
It marks the end of an amnesty which has twice been extended at Jakarta's request.
"The government is tegas (firm). There will be no deferment," Home Affairs Minister Azmi Khalid said at the weekend.
"When they are caught this time, not only will we haul them to court but they will also be barred from entering Malaysia in future."
Arrest and punishment
He warned Malaysian employers, who sometimes prefer illegal workers because they can pay them less than locals, also faced arrest and punishment under tough laws introduced in 2002.
The crackdown will be Malaysia's largest blitz to flush out illegal immigrants in three years. A similar nationwide sweep was carried out in 2002 following the end of a four-month amnesty programme.
Before the recent amnesty began on 29 October last year, Malaysia estimated there were more than a million illegal workers in the country, mostly from Indonesia but also from the Philippines, Myanmar, Bangladesh, India and Sri Lanka.
"The very reason we are sending them back is because we want them to come back legally. This is very, very humanitarian"
Home Affairs Minister
Nearly 400,000, mostly Indonesians, left without facing any penalty during the first three months of the amnesty, but others have remained, clinging to jobs in the construction, plantation and service industries in the face of unemployment at home.
The planned crackdown, which will involve about 500,000 officials and civilian security force volunteers, has been widely criticised by human rights groups which say it is open to abuse.
Indonesia and the Philippines have urged Malaysia to ensure there were no human rights abuses when it carries out the crackdown.
Amnesty International earlier this month urged Malaysia to halt the planned deportation of illegal immigrants amid fears some could face execution or torture in their home countries.
Migrants from Myanmar, Nepal and the Indonesian province of Aceh could be subjected to serious human rights violations if they were sent home in the crackdown, it said.
But Azmi said the government has been very humane and would ensure that the welfare of the immigrants was taken care of.
"There is no other country in the world that has come up with the amnesty programme like what we have. We have been very very humane with the illegals," he said.
"The very reason we are sending them back is because we want them to come back legally. This is very, very humanitarian."