Political scholar Ma Ngok, of Chinese University's department of government and public administration, said Cheng's comments did not come as a great surprise.

'They want to keep their distance from Leung because they're doubtful about how popular he is going to be with Hongkongers in the long run,' Ma said.

The unionists probably doubted Leung's labour proposals, such as studying standard working hours, would turn into meaningful changes for Hongkongers, he said.

Cheng discussed strategy in view of the Legislative Council election which will be held in September, and the importance of retaining the federation's talented members.

'Our talent is limited. There is no point quitting your job as a district councillor to become an official, and then losing in the next election,' Cheng said.

The 368,000-member federation has four seats in the legislature, and Cheng said earlier that it aimed to contest all five geographical constituencies, one of the five new seats in the functional constituency for district councils and two seats in the labour functional constituency.

Cheng is also a member of the Executive Council, of which Leung was convenor. Cheng said he would stay on the council if Leung invited him to.

Cheng, who has been involved in the federation's management for nearly 40 years, said it played a valuable role in scrutinising the government from both inside and outside the establishment - lobbying lawmakers while organising and taking part in social movements.

He said the public must not discriminate against people like Chen Ran, a mainlander whom Leung has hired as a project officer. Critics have faulted the appointment because Chen was a member of the Communist Youth League and is not yet a Hong Kong permanent resident.