PROVIDENCE, R.I. – The high-stakes legal dispute over Rhode Island’s public retirement overhaul faces a key court date Friday when attorneys for the state will ask a judge to dismiss a challenge from public-sector unions unhappy with the sweeping pension changes.

The unions argue the state is reneging on promised benefits and that lawmakers should have explored alternatives or negotiated concessions with workers before approving the pension law in 2011. State leaders insist that without the changes, ever-escalating pension costs would swamp state finances.

The lawsuit is being watched closelyas states seek to rein in pension costs. Collectively, states face a $1.4 trillion gap between what they’ve promised workers and what they’ve set aside to pay for those benefits.

Superior Court Judge Sarah Taft-Carter will hear arguments from both sides as she considers the state’s motion to dismiss the unions’ legal challenge. A ruling on the motion is not expected immediately.

The new law is intended to save an estimated $4 billion over 20 years by suspending retiree pension increases, raising retirement ages for many workers and creating a new benefit plan combining traditional pensions with 401(k)-style accounts. Before the changes were enacted, the state’s pension costs were set to jump from $319 million in 2011 to $765 million in 2015.