He said he would only allow it if lawmakers enact a series of revisions -- including one to cap sick time payouts that can send workers into retirement with six-figure "golden parachutes."
Those provisions prompted police and firefighter unions to accuse Christie of trying to kill the legislation.
The bill passed with strong bipartisan support over the objections of some who warned spinning off management of the pension fund but not the liabilities put taxpayers at risk.
According to the message accompanying the conditional veto, Christie shared those concerns, saying his proposed changes would shield taxpayers from picking up the tab if the fund goes south.