Sparking a flare-up of simmering tensions this week, a Victorian union safety officer has become the subject of a criminal investigation after he tested the stability of a guard rail during a site visit and it immediately collapsed.

A letter from the AFP, seen by Fairfax Media, details the allegation of property damage against the Construction, Forestry, Mining and Energy Union's Peter Clarke. The union said the case was "bizarre" and added to serious concerns that police were responding to political pressure to become more heavily involved in industrial relations matters.

"This is a bizarre use of AFP resources that ought to be used to deal with the serious criminality that goes on in the community," union secretary Dave Noonan said.

"It's clear to us that senior officers of the Australian Federal Police are directing some kind of campaign against the union and its officials."

The case is the latest example of what the CFMEU claims is unjust, heavy-handed treatment of its members and officials in Victoria, the ACT and Queensland by the federal police. Slater & Gordon, the union's legal firm, has filed a formal complaint against the AFP with the Commonwealth Ombudsman.

Video footage of the alleged property damage incident shows Mr Clarke – a safety officer with the union's Victorian branch – approaching the guard rail during a safety inspection at a Canberra construction site in February. It appears to show him momentarily shaking the railing before a large section collapses.

Mr Clarke has been called in for interrogation over the incident.

"During the course of the investigation, Mr Clarke was identified as being responsible for damaging a guard rail at that location," AFP acting Commander Robert Wilson said in the letter.

"The allegation against Mr Clarke is property damage ... Police wish to speak to Mr Clarke in relation to the matter in the form of a record of interview."

The union said falls from heights were a leading cause of workplace injury and death, and every safety official was expected to check the stability of guard rails during site inspections. Statistics from Safe Work Australia shows the nation's construction industry accounts for almost 40 per cent of fall-related deaths.

"The fact that this rail was so flimsy it didn't survive a light shake shows it would have been completely ineffective in preventing a fall, and completely fails to comply with the relevant codes of practices," Mr Noonan said.

"Are our priorities saving workers on construction sites from getting killed, or trying to cover up for builders who cut corners on occupational health and safety and put workers' lives at risk?"

The Australian Federal Police said the investigation was ongoing and it would not be appropriate to comment.

Federal and state police have been investigating alleged criminal conduct involving current and former CFMEU officials after a series of referrals from a recent royal commission. Victorian branch leaders John Setka and Shaun Reardon have been charged with blackmailing concrete company Boral.

But prosecutors were embarrassingly forced to drop another high-profile blackmail allegation against union organiser and former rugby player Johnny Lomax, who was charged over comments made in enterprise bargaining negotiations. Mr Lomax is taking the AFP to the ACT Supreme Court in an effort to force it to disclose information about its failed case against him.

Do you know more? Email n.toscano@fairfaxmedia.com.au