A second Construction, Forestry, Mining and Energy Union (CFMEU) official has been arrested in relation to evidence presented to the trade union royal commission in Canberra.

Former Canberra Raiders NRL player and CFMEU official John Lomax, 49, was arrested by officers over alleged blackmail claims.

He is yet to give evidence at the trade union royal commission.

However, evidence over the previous two weeks has pointed to union officials intimidating building contractors in the nation's capital.

It comes after former CFMEU official Fihi Kivalu was arrested on blackmail charges following allegations heard at the commission last week that he had demanded bribes from ACT builders to secure them work.

Kivalu pleaded not guilty to the charges and was released on bail.

Lomax played 65 games with the Canberra Raiders and was named the team's player of the year in 1994.

CFMEU describes arrest as 'an absolute disgrace'

CFMEU national construction secretary Dave Noonan released a statement which said Lomax had been trying to negotiate better pay and conditions for workers.

"Mr Lomax was denied the right to have a lawyer present during the time he was at the police station," it said.

"He has not been provided with any written document setting out allegations against him.

"Mr Lomax was told by police that he was accused of forcing an employer to enter into an [enterprise bargaining agreement] and that as a result the employer suffered financial loss due to paying workers higher wages.

"No allegation has been made that Mr Lomax obtained any personal financial benefit."

Lomax has been released on watch-house bail and will face the ACT Magistrates Court next month.