George Alex to front unions commission

Underworld figure George Alex is set to appear before the Royal Commission into Trade Union Governance and Corruption.

Mr Alex will give evidence on Wednesday after the commission on Tuesday heard tapped phone calls between him and a construction union official.

The commission also heard a recording on Monday of construction union organiser Darren Greenfield telling union delegate Mario Barrios that Mr Alex was "weak" and he would "front" him if Mr Barrios was worried after Mr Alex phoned him in August 2014.

"I've had to work with these dogs for f***ing two years now, mate. It's been the worst two years of my f***ing life," Mr Greenfield told Mr Barrios on August 21, in a phone call played to the court.

The commission is investigating links between the Construction, Forestry, Mining and Energy Union and Sydney-based Mr Alex as part of an inquiry into phoenix companies - companies that collapse owing worker entitlements then re-register under a new name.