The Construction, Forestry, Mining and Energy Union called in the independent safety regulator to check the site after concerns about a trench in front of the Commonwealth office block.

Union secretary Dean Hall said workers were concerned about the potential of the trench to subside during rain.

Workers had also been concerned about an incident when an excavator ran into the front of the building, causing minor damage.

Work Safety inspectors attended the site on Tuesday where they issued two prohibition notices, requiring an immediate stop-work, as well as a further five improvement notices.

The company, Woden Constructions, was asked to provide WorkSafe with a geotechnical report on the trench.

The company was also ordered to require a subcontractor to repair a machine, while improvement notices were issued on safety fencing and signage, particularly relating to pedestrian access.

WorkSafe also noted it was unacceptable to have workers cross Constitution Avenue to access first aid and toilet facilities.

ACT Work Safety commissioner Mark McCabe said Woden Constructions was an experienced company and he was surprised by the number of notices issued on Tuesday.

The company's managing director, Peter Middleton, said the notices were for minor issues and the company had “an excellent safety record”.

“Whilst we are always happy to receive constructive safety input from the CFMEU, we reject safety being used as an industrial weapon in pursuit of an EBA, which some of our employees believe has occurred in the past,” he said.

He said a geotechnical report conducted on Tuesday afternoon had found the trench "perfectly safe, with no signs of instability''. The report would be given to WorkSafe.

“Prior to this matter becoming public, Woden’s staff was working constructively with WorkSafe to discuss the contents of the notices,” Mr Middleton said.

But Mr Hall said the company needed to raise its safety standards, not only to protect its workers but to ensure the safety of the considerable pedestrian traffic that passed through the work site each day.

“Mr Middleton can say what he likes about the union, but the fact WorkSafe has issued such a large number of notices shows there is clearly something wrong,'' he said.

Mr McCabe said the company had been working with WorkSafe to address its concerns and he would be organising follow-up inspections.