A driver who sued local traffic police for legal recognition of his innocence said he has received threats pressing him to withdraw the case.

Zhang Hui, a white-collar worker in Shanghai, was fined 10,000 yuan ($1,470) in September by local traffic management authorities of the Minhang district for operating an illegal cab service.

Zhang immediately brought the local traffic police to court, alleging that the police obtained evidence against him by adopting an illegal entrapment scheme.

According to Zhang, on Sept 14, he was stopped by a pedestrian who claimed to be suffering from a severe stomachache. Zhang turned the man away at first, but eventually gave in because the man appeared to be seriously ill.

During the short drive, Zhang twice declined the man's offer to pay. When Zhang stopped at a turn, the passenger snatched his car key. The police arrived, dragged Zhang out of his car, and charged him with operating an illegal taxi service.

In late October, the local traffic police withdrew the charge, returned the fines and apologized to Zhang, after Sun Zhongjie, a 19-year-old migrant worker, cut his small finger to call public attention to his own case, thus setting off official investigations in Shanghai.

Despite the acquittal, Zhang decided to go ahead with the lawsuit against Minhang district traffic police for vindication of the law.

However, his wife received a letter early this week, in which the individuals who threatened Zhang also claim to have details about his family, including his parents and 5-year-old daughter, according to Zhang. He believes that the letter came from someone who worked with the local traffic police in its entrapment scheme.

According to the letter posted by Zhang on tianya.com, a popular online community in China, the anonymous sender claimed that he and his colleagues have failed to earn money for one month since the exposure of the entrapment cases.

"Zhang has received an apology from the government and the refund of fines, which proved his innocence. Please drop the case and let us make a living " the letter reads.

Zhang, in a telephone interview with China Daily on Friday, said the letter has infuriated him.

"I feel threatened," Zhang said. "I don't want to elaborate on that, but who knows what action they might take in the days to come," he said.

He vowed he would not withdraw the lawsuit because of the anonymous threat.

The illegal entrapment cases, which have also occurred in other parts of Shanghai, which were disclosed recently, have garnered widespread attention.

The Pudong New District government issued a public apology on Oct 26 to Sun Zhongjie.

Zhang's case has also led to a heated discussion among netizens, most of whom have supported Zhang and expressed concerns of the safety of his family.

An officer of the publicity office of Minhang district, who declined to be identified, said: "We regard it a personal issue (concerning the letter Zhang received). Let's wait and see the final judgment next week."