A construction company manager has been arrested amid a war between builders and unions in Victoria.

A site manager at Melbourne building firm VCON was arrested after a 26-year-old Trades Hall employee received a disturbing email in her inbox last week.

“F*ck off you scum c*nt,” the email treatise began.

“If you continue to attack my livelihood I will track you down and attack you and your family!! This is your first and final warning!!”

The sender has been charged with the criminal offence of using a telecommunications service to menace, and released on bail.

VCON and associated firm Element Five have been the targets of a campaign by the CFMEU union and Trades Hall officials.

The unionists say the companies’ “shocking” safety standards have to be highlight, including a workplace death, 104 “serious incidents” and 23 improvement notices it has received in the past two years.

Trades Hall organisers have handed out flyers outside an Element Five work site in combination with an email and petition campaign.

Reports say the menacing email was sent by the site manager in response.

“I sent an email inviting people who had signed the petition to join us at a street stall in the CBD,” the Trades Hall organiser told Fairfax.

“At first I was confused why someone who had signed the petition calling for better workplace safety would be writing this to me, and then I read his email signature. I'm shaken by his violent response.”

The CFMEU has been under fire after remarks of its secretary John Setka appeared to suggest he would track down inspectors of the federal building industry watchdog, the ABCC.

“Let me give a dire warning,” Mr Setka told a crowd of protesters last week. 

“When we come after you, you'd better be careful.”

Setka said he wanted to “expose them all ... lobby their neighbourhoods ... go to their local footy club”.  

The head of the Australian Building Construction Commission (ABCC) has referred Mr Setka's comments to the police.

“A whole new low was reached even by Mr Setka's standards yesterday, when he targeted the kids of the ABCC inspectors,” said Employment Minister Michaelia Cash.

Setka has issued a statement claiming the comments were “deliberately taken out of context by the Liberals”, and that his speech reflected the “depth of anger” workers felt about alleged persecution by the ABCC. 

“But as a family man and father of three beautiful children, if my comments were taken out of context, or if they came across in a manner that was threatening, then I truly apologise,” he said.

The CFMEU was hit with heavy penalties in 2015 after it threatened Element Five and illegally blocked access to a Hawthorn building site in its push to set up a union enterprise agreement.

The union was fined $28,500 for acts of coercion, and a former union official was ordered to pay penalties of $8500.