MILWAUKEE — Early returns show Wisconsin's Supreme Court election is very close.

The initial returns Tuesday night showed Wisconsin Supreme Court Justice David Prosser locked in a virtual dead heat with challenger JoAnne Kloppenburg. The race has become a referendum on Republican Gov. Scott Walker's contentious new union rights law.

Kloppenburg's campaign has surged over the last several weeks as her supporters worked to focus anger over the new union law onto the conservative-leaning Prosser. They hope a Kloppenburg victory will tilt the Supreme Court to the left and set the stage for the court to strike down the law.

The law strips most public workers of nearly all their collective bargaining rights. Walker has said the move is needed to help balance the state's budget. Democrats say it's designed to cripple unions.