A Hong Kong politician has said he was pressured to bow out of a city election to clear the field for a candidate favoured by the Chinese government, which, if confirmed, could offer rare evidence of interference by Beijing in city politics.

Hong Kong, which has a special autonomy in China, held an election for a city legislature on Sunday, its first major test of public opinion since pro-democracy protests in 2014 ignited calls for independence, especially among young voters.

Ken Chow of the pro-business Liberal Party told Reuters on Wednesday he withdrew from the election after three men he believed were sent by the Chinese government threatened him while he was visiting the city of Shenzhen in August.

“They said I must stop campaigning. They also said I must leave Hong Kong as soon as possible … and I was only permitted to come back after the results,” Chow said. “They said, ‘If you keep being stubborn, we will take action, and your supporters will pay a heavy price.'” Reuters was not able to independently corroborate Chow’s account.

China’s main representative office in Hong Kong, the Liaison office, gave no response to faxed questions. China’s Foreign Ministry spokeswoman said she had no real understanding of the issue.

Chow, who campaigned as a pro-establishment candidate, said other people, whom he declined to identify, had offered him money to withdraw from the election, in order to leave the field open for a pro-Beijing candidate. “They said ‘you don’t have a chance to win. If you really participate in the election, you’ll only ruin the grand plan’,”Chow said.

The former British colony returned to China in 1997 under a”one country, two systems” agreement that ensured its freedoms. But Beijing has ultimate control and some Hong Kong people are concerned it is increasingly interfering to head off dissent.

In late August, Chow announced he was dropping out of the race but did not say why. The pro-Beijing candidate he would have competed for votes with won a seat on Sunday.

Chow’s party told media in August the Independent Commission Against Corruption (ICAC) would investigate whether he had been threatened.

The party said on Wednesday its honorary chairwoman and Hong Kong deputy of China’s National People’s Congress, Miriam Lau, would write to China’s head of parliament to urge the Beijing government to investigate.

The ICAC said it would not comment on individual cases but it placed great importance on election fairness.

Hong Kong’s Secretary of Justice, Rimsky Yuen, told reporters on Thursday he could not comment on individual cases but he trusted the ICAC would follow up, even though it was hard to investigate events that took place outside Hong Kong.

“If we think there is evidence showing there may be corrupt behaviour relating to the elections, I think our government has the duty and the need to follow up,” Yuen said.