WASHINGTON — The Supreme Court’s conservative justices signaled during oral arguments Monday that they will vote to strike down another campaign funding law and make clear that states and cities may not try to “level the playing field” between candidates for public office.

The justices objected to part of an Arizona law that provides public funds to candidates for state office if they agree to forgo private fundraising. The disputed provision gives extra “matching funds” to candidates who face a well-funded and free-spending opponent.

Conservatives and libertarians in Arizona sued and argued that these extra funds unfairly penalized candidates who relied on private fundraising. They lost in the U.S. 9th Circuit Court of Appeals, which upheld the law and said it did not limit the free speech rights of the candidates who depended on private funds.

The Supreme Court has been split 5-4 on campaign funding cases, with the conservative bloc in the majority, and that split was evident again Monday.

Arizona’s voters adopted the Citizens Clean Elections Act in 1998. Several states, including Maine, Connecticut and Florida, adopted similar laws, as have at least a dozen municipalities.

“Under our precedents, leveling the playing field is not a legitimate state purpose,” said Chief Justice John Roberts.