AUGUSTA – Despite expressing support for similar measures in the past, Maine’s two Republican senators voted with their party Tuesday against beginning debate on a campaign finance reform measure.

Sens. Olympia Snowe and Susan Collins said the Disclose Act would treat large politically active groups, such as unions and corporations, with two different sets of rules.

Democrats fell short of the 60 votes needed to bring the bill to a vote in the Senate. It was passed by the House in June.

The measure was drafted following a U.S. Supreme Court ruling in January that eliminated restrictions on political advertising that were included in a 2002 campaign finance law known as McCain-Feingold. Both Snowe and Collins voted for that law. The court ruling means corporations and other special interest groups can make unlimited donations for campaign advertising.

“Under the Disclose Act, unions are exempt from certain disclosure and disclaimer requirements, but these same requirements are imposed on companies,” Snowe said in a statement. “And, the bill does not apply to corporations that own media outlets, which would allow certain large corporations to enjoy unrestricted speech.”

Collins, a co-sponsor of the McCain-Feingold law, called the new legislation a “partisan proposal.”

She said a defense contractor would not be able to finance independent campaign expenditures, but the union representing the contractor’s work force would be able to do so.

A recent poll showed that 85 percent of Mainers support increased campaign financial disclosure and transparency and some local activists say they hope Snowe and Collins seek to compromise with Democrats.

“The League of Women Voters is very disappointed that this isn’t coming before the Senate at this time and we hope that after the recess that our senators will work to bring about a bipartisan agreement,” said Barbara McDade, president of the League of Women Voters of Maine.