UCATT head George Brumwell, who branded the employer body "pariahs" in the safety world, said the confederation should put aside its anti-trade union animus and show some leadership by taking part in the trials.
The scheme is expected to begin early next year and cover three pilot areas.
Brumwell said: "We don't believe that the Construction Confederation represents the views of the responsible elements of the industry. These are the views of the weakest link.
"It obviously never intended to allow these pilots to take place and has acted in staggeringly bad faith by stringing everyone along – including the government ministers who backed the pilots – and must feel deeply embarrassed."
Construction Confederation chief executive Stephen Ratcliffe retorted that its position had always been clear and said he was surprised and disappointed by Brumwell's language.
The confederation’s views are those of the weakest link
George Brumwell, UCATT
He said the confederation had explained repeatedly why it did not support the scheme and to suggest it had been stringing people along before pulling out was completely wrong.
He said: "We have been very active in expressing our views throughout on this matter and since first mooted in 1997 we have indicated our concerns at consultative meetings."
The confederation says the roving reps scheme is flawed because it will not provide a yardstick for measuring improvements in safety standards.
He said the confederation always valued the opportunity to discuss matters of vital mutual concern with the trade union side but would not and could not support the scheme. He added that, as currently proposed, the scheme did not offer a realistic prospect of success.
The Construction Confederation, he said, had led the way in taking positive measures to drive forward the health and safety agenda.