AUGUSTA – A conservative think tank that backed a government-spending cap referendum should have disclosed more information about its activities during the fall campaign, according to the state’s campaign finance watchdog panel.

The Commission on Governmental Ethics and Election Practices issued its ruling Wednesday in a case filed against the Maine Heritage Policy Center.

The commission said the policy center should have filed a form that discloses how much time and money it spent to persuade voters to support the Taxpayer Bill of Rights. The proposal, known as TABOR, was defeated at the polls.

In its 4-0 decision, the commission gave the policy center 30 days to file the information. Commission member Jean Ginn Marvin, a Republican, did not vote because she’s treasurer of the Portland-based think tank.

The complaint was filed by Carl Lindemann, who contended the policy center should have formed a political action committee to handle its role in the citizen initiative.

The Texas resident is likely to appeal the ethics commission decision, said his lawyer, John Branson of Portland.

Bill Becker, executive director of the center, said it participated in several forums and spoke to the media about the value of the initiative. But it did not spend money on television, radio or newspaper advertising, and it did not conduct a mass mailing, he said.