The U.S. Supreme Court derailed a key part of Arizona's campaign finance system on Tuesday by at least temporarily blocking extra money for publicly funded candidates outspent by privately financed rivals or targeted by independent groups' spending.

The court said in a brief order that it will prevent the state from using its system of so-called matching funds at least until the justices decide whether to hear the full appeal of opponents of the key provision of the state's campaign funding system.

Distribution of matching funds was to start June 22, but it could be the fall before the court decides even whether to accept the case. Arizona's primary election is Aug. 24.

Publicly funded candidates get matching funds when they're outspent by privately funded rivals or targeted by independent groups' spending.

Critics contend matching funds chill free-speech rights of privately financed candidates and their contributors by inhibiting fundraising and spending. State officials defend matching funds, saying they help combat contributions-for-favors corruption and encourage more people to run for office. Also, blocking matching funds would be disruptive to candidates already committed to running with public funding, officials argued.