A joint AFP and Victoria Police investigation into union corruption and criminality will act “without fear or favour”, Victorian Premier Denis Napthine has said.

In Melbourne to launch the task force with Premier Napthine on Friday morning, Prime Minister Tony Abbott said construction sites had been places of “violence and lawlessness” for “too long”.

“There could hardly be a graver claim against sections of the union movement,” Mr Abbott said.

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“Victoria Police intelligence indicates that criminal activity is undertaken by union officials directly.”

Mr Abbott said the royal commission into union corruption had exposed evidence of blackmail, corruption, intimidation and violence.

He said commissioner John Dyson Heydon wrote to him several weeks ago, asking for a police task force to be established.

When asked whether a police task force was necessary, the prime minister said intimidation of witnesses had been a significant issue during the royal commission.

“While royal commissions do have extensive powers, police have much wider powers when tackling and investigating criminal behaviour,” he said.

“Police can also protect witnesses. Intimidation of witnesses has been a significant issue.”

Mr Napthine said illegal activities in the construction industry were blowing out the cost of infrastructure, hurting Australians.

“These illegal activities add cost to infrastructure projects, add cost to private building construction and they hurt all Victorian and Australian families.”

Opposition leader Bill Shorten said the announcement was politically motivated by the upcoming Victorian election in four-week’s time.

The Napthine Liberal government is set for a thumping at the election, trailing Labor by 10 basis points, according to this week’s Ipsos poll.

“What the prime minister has announced today is exactly what I announced nine months ago,” Mr Shorten said.

“I suspect that today’s announcement and the timing of it is more to do with Victorian electoral politics.”

Construction, Forestry, Mining and Energy Union (CFMEU) national secretary Dave Noonan said the union would cooperate with police to help stamp out criminality, but labelled the task force a ‘political stunt’.

“I think it’s also important that the police be allowed to do their job with their own priorities and not being directed politically,” Mr Noonan said.

“Quite frankly, I think what we’re seeing today has some of the hallmarks of a political stunt.”

Australian Council of Trade Unions assistant secretary Tim Lyons also lambasted the task force as a stunt, saying the prime minister shouldn’t be directing police action.

“It shouldn’t be a matter for the prime minister or the premier or the attorney-general or any other politician to be saying what the police should do,” Mr Lyons said.

“Once you get politicians directing policeman, you’re halfway to corruption.”