But Comcare, which has been probing consistent reports of dangerous work practices at Cotter, denies allegations that it leaked to the job's bosses the names of workers who made complaints. Tensions between the union and the consortium building the dam, the Bulk Water Alliance, have been simmering since last year.

But they boiled over in November after ACT authorities shut down a large crane on the site on safety grounds and a worker went public with his worries.

The trouble has developed with the CFMEU complaining that staff expressing concerns are being targets for reprisal or even dismissal and in the latest escalation, the union's ACT branch secretary has accused Comcare of handing over records of confidential interviews with workers to their bosses.

Comcare is the regulatory authority that polices one of the BWA's members, building giant the John Holland group, which is ''self insured'' under the Comcare scheme.

Mr Hall has alleged in a letter to Comcare chief executive Paul O'Connor that one of the authority's investigators conducted several interviews with men on the site late last year, hearing concerns about safety, and then handed the material, with the names of the witnesses included, to a site manager.

''Prior to the interview our members were instructed by Comcare that the investigation was independent and that our members would not suffer any repercussion as a result of providing Comcare with an honest and open statement regarding the safety practices at Cotter Dam enlargement,'' Mr Hall wrote.

''We are at a loss as to how Comcare would send a copy of a confidential statement to an entity which is the subject matter of the investigation regarding a breach of safety procedures.''

But in a statement issued to The Canberra Times yesterday, Mr O'Connor dismissed the union's allegations and said that the men on the site had been afforded procedural fairness.

''The issues discussed with John Holland were of a general nature as part of usual investigation processes,'' Mr O'Connor said.

''No specifics or names were included.

''All of those interviewed have been given a copy of their interviews in accordance with Australian Government Investigation Standards.

''Comcare always complies with these standards.''

Mr O'Connor confirmed his inspectors were conducting an inquiry at the Cotter site but said it was being undertaken in accordance with the appropriate standards.