The four Catholic bishops of Massachusetts have endorsed ''Protect Marriage Sunday" — a one-day signature-gathering campaign that organizers hope will advance a 2008 ballot initiative banning same-sex marriage. The bishops have or will soon send letters to parishioners urging them to sign the petition.

A letter to this effect from Archbishop Sean O'Malley of Boston is expected in parishes this weekend, reported the Boston Globe.

''As faithful citizens, we have a moral obligation to defend the truth, no matter how counter-cultural or unappreciated our convictions might be," Bishop George Coleman of Fall River wrote in his letter to parishioners. ''The time is upon us to take a stand and to act, lovingly but firmly, to restore and defend the truth about marriage."

Christians of various denominations will participate in the coordinated effort on Oct. 2, and gather signatures at masses and worship services throughout the state. Organizers are seeking 120,000 signatures.

They are hopeful that enough signatures will be gathered on that day. Still, some churches are launching petition drives this weekend.

The Massachusetts Catholic Conference, Massachusetts Family Institute and Catholic Citizenship are backing the petition.

Larry Cirignano, executive director of Catholic Citizenship, told the Globe that he is confident the one-day campaign will be successful. However, he added, that it won’t be without opposition from some gay-rights activists, who are considering conducting ''truth-squadding," in which they shadow signature-gatherers and try to persuade people not to sign.

The signature campaign is also being opposed by the Religious Coalition for the Freedom to Marry, a group of more than 600 clergy, congregations, and faith-based organizations representing 21 denominations.

Last week, a separate 2006 measure that would have outlawed same-sex marriage and created civil unions was defeated in the Legislature.