Mahen has been a BCGEU member since 1992 when he started working at Riverview Hospital. Since becoming a steward in 1994, he has dedicated over 20 years to improving working conditions on union Joint Labour Management, Grievance Appeal, Equity and Bargaining committees. Mahen has worked countless hours to improve working conditions for Health Services workers within his local community. He served as chair and executive of Local 203 and executive member of Component 2 until the closure of Riverview Hospital in 2014. Then, he moved to the Forensic Psychiatric Hospital and joined Component 4.