It's 6 o'clock in the morning in a working-class neighbourhood in the Russian capital. Immigration officers are raiding a squat full of illegal workers.

There are half a dozen mattresses in each room and each person pays a rent of 70 euros a month to live in a dirty building that has already been condemned as uninhabitable.

They have come from the former Soviet republics of Central Asia to work on Moscow's many building sites.

"I know that half the workers on these building sites have no work papers," says Jamaat, a worker from Kirghizstan.

Without work papers they are paid much less than Russian workers and they have no way to defend their rights

“I was tricked,” says another young man. He was promised a salary of 800 euros but says he hasn't received a cent.

Without any legal papers, he risks being expelled from Russia and sent back to Turkmenistan.

But new legislation means it is fairly easy to get a Russian work permit.

"The employer doesn't even need to ask the permission of the migration service, he simply has to inform them that he is employing a migrant worker,” says Svetlana Gannushkina, head of the Civic Assistance Committee, a refugee advocacy group.

On Moscow building sites, migrant workers say they do not know the intricacies of Russian law and would not dare ask their employers to give them work papers.

“I don't have much of an education and I don't know Russian law," admits Azim, who came to Moscow from Tajikistan. "But I have been told that a work permit costs 150 euros.”

Another worker, Gulmira, told FRANCE 24 she paid an agent 300 euros for what she believed was an official document legalizing her status.

"They told me that it gives me the right to live and work in Russia for a year," says the young woman from Kirghizstan.

In fact, the document was a counterfeit passport which gives her no rights at all, so Gulmira still faces the risk of being expelled from Russia.

She won't be sorry to leave. Since she arrived in Moscow she has been living in constant fear of attack.

Ultranationalist groups hold regular demonstrations in the Russian capital calling for all migrant workers to leave.

According to estimates there are fewer than 2 million illegal workers in Russia, barely 2% of the active population.