Mining giant Rio Tinto, through its subsidiary Coal & Allied, is a shareholder in PWCS.
Workers at the Kooragang Island and Carrington sites have voted on a motion to take action and it has received strong support from the workers, MUA assistant national secretary Ian Bray says.
“PWCS anti-union proposals are seeking to undermine the safety and health of workers, tear up longstanding settlement procedure of contract issues, and radically change the scope of matters that can be arbitrated,” Mr Bray said.
Talks between union members and PWCS have been continuing for eight months.
Mining giant Rio Tinto, through its subsidiary Coal & Allied, is a shareholder in PWCS.