Federal police officers were called to a Canberra worksite last year to stop union officials entering during a concrete pour.
The Construction, Forestry, Mining and Energy Union claims the standoff started when its officials attempted to check worker certification and noticed safety breaches.
But the worksite's manager, Mainbrace Constructions, claims it had been subject to a campaign of harassment by officials trying to win jobs for union aligned companies.
The incident – which occurred during the construction of the Costco service station at Majura Park in November – will be examined by the Federal Court after the CFMEU filed a lawsuit against the site managers.
Court documents show the union alleges Mainbrace Constructions and its foreman breached the Fair Work Act by obstructing permit-holders from entering the worksite to inspect records and safety contraventions.
But Mainbrace Constructions, which will defend the lawsuit, claims the union officials were not entitled to visit the worksite.
Mainbrace Constructions disputed that the officials entered the site to inspect suspected safety contraventions.
The construction management firm instead alleges the CFMEU visited to inspect records but did not provide the required 24 hours' notice.
Permit-holders can enter sites with no notice if they reasonably suspect contraventions of the Work Health and Safety Act.
The CFMEU has asked the court to fine Mainbrace Constructions for each breach of the Fair Work Act and order that the union receive any penalties imposed.
The breaches carry maximum penalties of $10,000 for an individual and $50,000 for a corporate entity.
Court documents, filed by the union, say officials went to the site about 7am on November 11 as they believed some workers involved in a concrete pour had not completed compulsory certification and may not have been covered by adequate workers compensation insurance.
The foreman had been contacted the day before for confirmation on workers' status and informed union officials would attend the concrete pour.
The CFMEU alleges the site had only one access and egress, in breach of safety obligations.
The documents say the union officials saw workers under the concrete pump boom with no exclusion zone, placing them at risk if the boom collapsed.
Officials claim they waited and called to the foreman, but approached when they did not receive a response.
The foreman then allegedly told the officials to "get off the site", accused them of trespassing, and threatened to call the police to have them removed.
The officials told him they had a legal right to be there and he called the police, court documents said.
Police then arrived and blocked the officials from further entry.
But the foreman claims the officials pressured Mainbrace Constructions to use a company recommended by the union.
Court documents allege officials called the foreman a scab and threatened to "get" him and "stop the pour" days earlier.
During one conversation, the foreman alleges an official insisted Mainbrace use a CFMEU recommended company, saying: "Don't use [that operator], they're dodgy" and "You should have used … their EBA is with us."
The foreman said he called the police because the officials had entered the site unlawfully and refused to leave.
The matter is due for directions in the Federal Court in April.