Boston ? The state’s entire high court should decide whether to force lawmakers to take action on a proposed constitutional amendment to ban gay marriage, one justice decided Thursday.

Justice Judith Cowin made the ruling after hearing arguments on last week’s request by Gov. Mitt Romney and other gay-marriage opponents to force the lawmakers to decide whether voters can consider the proposal in 2008.

A hearing before the seven-member Massachusetts Supreme Judicial Court – the same panel that said gay marriage was legal in 2003 – was set for Dec. 20.

Supporters have gathered more than 170,000 signatures of people in support of the proposed amendment, which would define marriage as the union of a man and a woman. It would ban future gay marriages in Massachusetts but leave existing same-sex marriages intact.

Lawmakers postponed action on the proposed ballot question until January, prompting Romney’s request for court intervention.