March 11 (Bloomberg) — The second-largest U.S. teachers union has added a firm formerly headed by Bruce Rauner, a Republican leading the race in next week's Illinois gubernatorial primary, to its enemies list.

The American Federation of Teachers is urging public pensions to review investments with Chicago-based GTCR, a private-equity firm where Rauner was chairman before stepping down in 2012. He supports shifting government workers to 401(k)- type plans from traditional defined-benefit pensions, which give retirees a payout based on years of service and final salary.

The AFT, with 1.5 million members, is scheduled to release an updated "watch list" of 29 money managers that the union says support groups opposed to traditional pensions. GTCR has $4.9 billion of commitments from U.S. public pension funds, according to Preqin Ltd., a London-based research firm. The AFT is also adding Highbridge Capital Management and a unit of London-based insurer Aon Plc to the list.