Grocon, union blockade talks set to fail

Emergency talks to end an ugly Melbourne union dispute look set to fail, with developer Grocon unlikely to attend while the blockade continues.

Building giant Grocon doubts peace talks brokered by federal minister Bill Shorten will end union unrest that has paralysed major work sites - and has rejected Melbourne identity Mick Gatto's offer to act as a go-between.

Grocon CEO Daniel Grollo and Construction Forestry Mining and Energy Union (CFMEU) bosses are set to meet privately with Fair Work Australia on Thursday.

But if construction workers continue to defy court orders and blockade their Melbourne CBD building site, Grocon says it will walk away from the meeting organised by Workplace Relations Minister Bill Shorten.

"We have grave concerns attending talks while the CFMEU is still illegally blockading our site and preventing our workers from returning to work," a company spokeswoman said.

The stalemate prompted industrial negotiator Mr Gatto, who was acquitted of the 2004 murder of a hitman on grounds of self-defence, to offer his services.

"If they don't come to some sort of resolution, I'm sure they'll call me down," he told AAP on Wednesday.

"And if I get involved, I'm sure that will be the end of it."

Mr Gatto said he had helped craft the enterprise bargaining agreement for the union and Grocon as a key contact between CFMEU Victorian assistant secretary John Setka and Grocon's human resources boss, John Van Camp.

"They are both friends of mine," he said.

"But down the track Grocon really backflipped on the agreement."

Grocon rejected the idea that Mr Gatto had played a key role in the EBA and said his involvement was not needed.

"We will continue with the appropriate channels," the company spokeswoman said.

The CFMEU maintains its dispute is over safety concerns and Grocon's refusal to allow externally-appointed union stewards on Melbourne's Emporium construction site, though the company insists that is not the case.

The blockade began last week and then spread to Sydney on Wednesday where hundreds of workers lined Pitt Street and others maintained a presence outside another Grocon building site, though the NSW Supreme Court issued an injunction over the blockade at that location.

A day earlier, police clashed with Melbourne workers in scenes widely condemned by government and officials.

"If they want to make a point, there are ways of making a point peacefully," Prime Minister Julia Gillard told reporters on Wednesday.

Victorian Premier Ted Baillieu labelled the union's actions as "thuggish" and "unruly behaviour", while Grocon CEO Mr Grollo said such intimidating tactics were also "an illegal, absurd act".

But the union shows no signs of backing down and could not say on Wednesday when its protest will end.

"I haven't read any orders," state secretary Bill Oliver said of a Victorian Supreme Court ruling banning the blockade.

Fair Work Building and Construction confirmed on Wednesday that Grocon workplace disputes in Victoria, NSW and Queensland are being investigated.

The dispute continues amid claims and counter claims that bikies and organised crime figures have infiltrated many building sites.

Victoria's own building industry watchdog will investigate.

But Mr Gatto, who owns his own crane company, said widespread corruption has never been found.

"It's just a witchhunt," he said.