Immigration agents at Rio de Janeiro's airport are under investigation for allegedly accepting bribes to allow Chinese immigrants into the country illegally, Brazilian newspaper O Globo reported Saturday.

The Public Prosecutor's Office initiated the probe after a man who worked with the Chinese for the past 15 years tipped off the Ministry of Labor in July.

"Chinese fast food restaurant owners in Rio -- who recruit Chinese workers and maintain forced-labor-like conditions -- would spend up to 42,000 reais (around $12,000) for an illegal immigrant's entry," the tipster's report said, according to O Globo.

The witness recounted one incident in which a fast-food restaurant owner who was part of the corruption ring arrived at the airport 20 minutes after the time arranged with immigration officials.

Lacking payment, the officials had already sent the would-be immigrants back to China.

Last week, four Chinese workers kept in semi-slavery conditions were freed from a fast-food restaurant in Rio's northern suburbs by the Ministry of Labor, Globo reported.

According to information provided by the witness, the Chinese immigrants' passports are stamped by the immigration workers then "lost" to erase the evidence. The Chinese immigrants then receive new passports.

A source from the Public Prosecutor's Office told Globo that "the visas were probably falsified in China and when the immigrants arrived in Rio, the immigration department pretended to not notice that they were fake and would validate them, after payment of a bribe."

Federal police refused to comment on the case, Globo said.