Organisers of Sunday's anti-Occupy Central march will assign retired detectives to look into reports that some participants were paid to show up, after one participating group acknowledged it had offered money to marchers.
News organisations were also invited to provide more details to assist the investigation.
The organiser, the Alliance for Peace and Democracy, has so far confirmed one case of "protest recruitment". It said on Monday that a subsidiary group of the General Association of Hong Kong Heyuan Societies offered HK$380 to each person who joined its protest group, as Cable TV reported earlier.
The association admitted to "improper doings" in paying the protesters, and agreed to have its marchers excluded from the reported total, now at 193,000.
Sunday's march has been marred by reports in various media of some 10 organisations offering cash, free meals or paid transport to induce people to take part. The alliance has more than 1,500 mainly pro-establishment member groups.
A spokesman for the march's organising committee, Brave Chan Yung, yesterday said it was unfair to jump to conclusions based solely on news reports.
"We do not want to wrong a person if he is innocent, nor do we want to let a person escape responsibility if he has done wrong," Chan said. "We take the claims seriously and are inviting retired detectives to form a group to help us look into the reports."
At least three groups have denied resorting to freebies to recruit marchers.
According to the alliance, the Hong Kong Youth Association said that people featured in a Cable TV report on paid marchers were not its members.
A spokesman for the Hong Kong Shaanxi Friendship Association rejected a RTHK report that it had paid HK$800 per protester.
The Federation of Hong Kong Shenzhen Associations denied a Ming Pao report that it had paid people HK$300 each.