MOSCOW (AP) — Russian Prime Minister Vladimir Putin said Thursday that government officials must crack down on migrant workers who break the nation’s laws by failing to register or get work permits, and on companies that profit by hiring them.

Putin, who is campaigning for Russia’s March presidential election, was addressing an issue that angers many Russians because Moscow is overrun with immigrants who often sleep in basements and overcrowded apartments.

Some 10 million labor migrants, mostly from ex-Soviet Central Asia, flock to Russia visa-free annually. Many face abuses, low pay and enslavement, while their presence triggers xenophobia and hate attacks in a country where unemployment stood at about 7 percent last year.

Violent xenophobic groups have flourished in Russia over the past two decades. Their members kill and beat non-Slavs and anti-racism activists and crudely denounce the influx of immigrants from Central Asia and Russia’s Caucasus. Some Russians and nationalist politicians have accused the immigrants of stealing jobs and forming ethnic gangs.

Putin, who is expected to win the presidential election, said Thursday that people who violate immigration and labor laws should be barred from entering the country for up to 10 years.

He also said that Russians who profit by hiring and enslaving migrants, or by issuing fake work and residential permits, should face criminal charges instead of “symbolic fines.”

“We need to toughen sanctions against those who hire people without permits, basically as defenseless slaves,” Putin said in televised remarks addressing immigration officials.

He said that of the nearly 10 million foreigners now in Russia only 4 million work legally.

Ethnic Russians comprise two thirds of the country’s population of 142 million, but their birth rates are plummeting. The remaining third of Russia’s population are mostly from predominantly Muslim Caucasus.