A union executive says she was not trying to keep documents from a corruption inquiry when she ordered emails be deleted.

A construction union executive has denied she ordered the deletion of emails because a royal commission had demanded them as part of an investigation into corruption.

Kylie Wray, general manager of the NSW branch of the Construction, Forestry, Mining and Energy Union (CFMEU), told the Royal Commission into Trade Union Governance and Corruption on Tuesday she asked union staff to delete an unknown number of emails after a “disk space error” caused a crash that stopped the branch receiving external emails.

Up to nine people worked to delete emails over three days at the branch, starting from June 23, 2014, to free up space on the email system and get it working again, Ms Wray said.

There had been no backup for the email system since a May 2010 firebombing of the union office.

Counsel assisting the commission, Jeremy Stoljar SC, asked Ms Wray whether the urgent deletions followed requests from the commission for documents.

The commission sent letters to the CFMEU on May 30, demanding extensive records be supplied within one week, including any files relating to any enterprise bargaining agreements reached with companies operated by underworld-linked businessman George Alex.

On June 25 the commission wrote again, demanding electronic documents be supplied by July 1. The CFMEU’s solicitors replied that, in addition to the unworkable time frame, a number of emails had been deleted or lost because of the system crash.

Ms Wray denied she wanted to delete the emails which the commission wanted to see.

She told Mr Stoljar she had not considered filing emails on an external hard drive and deletion was “the only way we thought of at the time.”

CFMEU national construction secretary Dave Noonan said in a press release after the day’s hearing that the union had complied with the commission’s requests.

“There has been no attempt by anyone in the union to knowingly destroy documents relevant to the Royal Commission,” he said in the press release.

Mr Noonan also criticised testimonies from Fair Work Building Inspectors that they were abused when carrying out their work on construction sites.

Earlier, video evidence tendered to the commission captured Fair Work Building Inspector Seamus Flynn repeatedly being called a “f***ing piece of s***” by a CFMEU official at an Adelaide site after he arrived to check reports the union had entered without permits.

Video recorded by Mr Flynn’s partner showed a man Mr Flynn identified as CFMEU official John Perkovic standing close to him and shouting abuse.

In his statement, Mr Flynn said Mr Perkovic “quickly moved towards me, saying `you f****ing maggot, what are you taking a photo of me for you piece of s***'”.

On the video, Mr Perkovic can be heard saying: “You f***ing coward, I’d f***ing take you to school, you f***ing piece of s***”.

In his press release, Mr Noonan said: “Swearing on building sites is nothing new and doesn’t warrant a $53 million royal commission”.

The hearing continues on Wednesday.