The ICAC should investigate why Urban Services Department (USD) cleaning staff who slept and played cards during working hours were not exposed for more than a year, according to a report.
A Provisional Urban Council committee, which probed the case of lazy staff, said anti-graft officers should intervene.
Municipal councillors, acting on a tip-off, discovered the scandal in January.
Last year, the teams only transferred 0.32 tonnes of refuse a day. Since the scandal was uncovered, they have collected an average of 1.45 tonnes a day.
'The committee considers it was a group action. It is difficult to explain why such misconduct, which involved three groups of staff totalling 24 workers and some supervisory officers, could be covered up for more than a year,' a source said. 'It is impossible that no one in USD management noticed this. The committee considers it appropriate to probe whether corruption was involved.' It is understood the department strongly opposed the ruling, stressing workers' laziness was a matter of workplace culture and no corruption was involved.
But the committee, composed of six members from the Democratic Party, insisted on the wording.
The committee also condemned the department for not improving the workers' performance even though an internal report 14 years ago indicated a problem.
The Sunday Morning Post revealed last month that a 1985 report described worker productivity as 'extremely low'. It recommended an inspection team be set up, but the department ignored the call.
The council's report also suggested an inspection team to check workers' performance. Inspectors should lift manhole covers and take pictures to ensure cleaning work was being done.
A hi-tech device, similar to the black box installed in an airliner, should be installed in the 25 street-cleaning or drainage clearing vehicles to record every movement and detail of its operations.
The committee asked the Civil Service Bureau to investigate the case where the department's deputy director Michael Arnold allegedly attempted to stop a worker giving statements to the inquiry.
The witness, Law Pui-lam, testified his colleagues pumped tap water into tanks to make up their daily quota, cleared drains only once a week instead of every day, played cards or slept and returned to the office the next morning to sign the log book.
He would drive his vehicle around the streets to make up the mileage. He was supposed to take workers to clear drains every night.
Mr Arnold was later removed from the department. The report allocates three pages to criticising him.
The report raised concerns about Mr Law, saying measures should be taken to ensure he would not be discriminated against.
The report will be distributed to the USD and other related departments for a response tomorrow and will be released later this month.