A coalition of powerful unions, business interests, environmentalists and others has raised $740,000 in its effort to defeat this year’s ballot measure asking voters whether they want to convene a state constitutional convention, according to the latest campaign spending reports filed Monday.

The ballot measure committee, called Preserve Our Hawaii, has spent hundreds of thousands of dollars of those funds on radio, print, television and digital ads in recent weeks urging residents to vote “no” on the ballot question.

The latest filing by the group shows that the Hawaii Government Employees Association donated $50,000 to the committee, increasing the amount that the union has contributed to $290,000. The United Public Workers contributed $25,000.

Other unions that have made contributions include the Hawaii State Teachers Association, the Hawaii Fire Fighters Association, the University of Hawaii Professional Assembly and National Education Association.

While contributions have come from unions, the coalition also includes the Hawaii Democratic Party, the Chamber of Commerce Hawaii, Sierra Club Hawaii and the Hawaii chapter of the American Civil Liberties Union, among others.

Many of the groups opposed to the convention could stand to lose something if the state Constitution is altered. Opponents have argued there is too much at stake to open the Constitution to revision, particularly when it comes to protections for labor, the environment and Native Hawaiians. Some have also worried that money and special interests could unduly influence a convention.

Proponents have argued the state Constitution was meant to be periodically revised and that a convention could help restore trust in government and provide an opportunity to push forward reforms the Legislature has been reluctant to take up, such as campaign finance reform and establishing term limits for state legislators.

There hasn’t been a comparable, organized effort to drum up support for a constitutional convention, though individuals such as state Sen. Laura Thielen have publicly expressed their support.

The last time a constitutional convention was held in Hawaii was in 1978. The ballot measure is put to a vote every 10 years. In 2008 the convention proposal was defeated 62 percent to 34 percent, with about 4 percent of voters leaving the question blank.

If it passes today, delegates will be chosen during the next election or a special election called by the Legislature. Any amendments arising out of the convention would need to be approved by voters.

A simple majority of votes is required for the measure to pass, though blank votes will be counted as “no” votes.