MOSCOW - Russia began cracking down on millions of illegal workers as tough new migration rules went into effect yesterday amid a rising tide of anti-immigrant sentiment.

But with Russia's population plummeting, there is concern that the country could face serious shortages of low-wage laborers.

"They don't like the color of our skin here," said an Azerbaijani produce seller at a Moscow food market who gave his name as Alek. He predicted that he and many of his fellow migrants would have to leave Russia.

Under the new rules, which set a quota of six million foreign workers for 2007, authorities are carrying out strict checks of the 10 million to 12 million foreigners who are already working in Russia, most illegally.

The legislation eases stringent procedures for citizens of most former Soviet republics who enter Russia starting yesterday to obtain work permits, but it also increases fines for businesses that employ illegal migrants.

Further limiting foreigners' right to work in Russia, a government decree that took effect Jan. 1 restricted the number of non-Russians in the retail trade.

The issue of immigration has become a lightning rod for President Vladimir V. Putin's government amid growing popular resentment of migrants - in particular, darker-skinned workers from former Soviet republics in the Caucasus and Central Asia.

Racist attacks and hate crimes are on the rise.

Critics warn that the authorities' moves will only encourage xenophobic sentiment, fuel inflation, and accelerate Russia's population decline.

The population is dropping by about 700,000 a year and has fallen below 143 million, a demographic crisis attributed to the economic turmoil that followed the Soviet collapse. The decline would be even more catastrophic were it not for immigration.