HELENA — The U.S. Supreme Court, in a 5-4 decision Monday, summarily reversed a Montana Supreme Court ruling and struck down the state’s century-old ban on corporate spending for or against political candidates.

The ruling opens the door for corporations and unions to spend directly from their treasury on advertising and other independent expenditures promoting or opposing candidates in state office elections in Montana this year, for the first time in 100 years.

Some Montana officials denounced the ruling, calling it a “blow to democracy” and vowed to fight it.

“I thought it was a sad day for democracy and for those of us who really believed that the U.S. Supreme Court is something more than another political body in Washington, D.C.,” said state Attorney General Steve Bullock, who unsuccessfully defended Montana’s law.

Bullock, a Democrat running for governor, added: “We have a law that has served us well in Montana for over 100 years, and I think our elections and our participation are markedly different.”

Gov. Brian Schweitzer also blasted the decision.