Boston-area religious leaders are urging voters to reject Ballot Question 4, which would legalize recreational marijuana in Massachusetts. And Boston Cardinal Sean O’Malley is leading the push—once again putting his political clout to the test on a highly contentious issue.

O’Malley asked other faith leaders to sit down and strategize two weeks ago. That planning session led to an open letter, released yesterday, in which more than 130 ministers, imams, rabbis and lay leaders made the case for an anti-Question 4 vote.

That was followed by an ecumenical event Tuesday afternoon, at Dorchester’s Deliverance Temple Worship Center, at which several men and women who signed the letter made their case in person—and O'Malley stole the show. His leadership role was cited by other speakers. He was the last religious leader to speak, followed only by Boston Mayor Marty Walsh and Massachusetts Governor Charlie Baker. And he offered the prayer of adjournment—asking God to “touch the hearts of our people as they in conscience cast their ballots next Tuesday, so that this terrible scourge will be avoided in our Commonwealth.”

In his brief speech, O’Malley described marijuana as a gateway drug that carries its own significant health risks. (He mentioned pregnant women and newborn children as especially vulnerable groups.)

O’Malley also warned that a “Yes” vote on Question 4 would exacerbate the state’s ongoing opioid epidemic, citing his experience as a prison chaplain, inner-city priest, and Bishop of the West Indies.

“In each of those venues I saw what drugs did to my people,” O’Malley said. “I saw how marijuana was so often the initiation into a life of drugs.”

Afterward, speaking to the media, O’Malley said he hadn’t taken the possibility of a “Yes” vote on Question 4 seriously until recently. 

“I guess I was sort of lulled into a false sense of security thinking that this initiative would never get legs,” he said. “And then when I heard how it was going, I thought, ‘We can’t just sit idly by.’ So we reached out to the other faith communities, and I was amazed at the response.”

Asked about a key pro-legalization argument—that the enforcement of drug laws disproportionately affects people of color—O’Malley replied: “You don’t respond to one problem by creating other problems that are more serious.”

O’Malley’s record in recent political battles is mixed. Four years ago, his advocacy helped defeat a proposal to legalize physician-assisted suicide in Massachusetts. But in 2014, a ballot question that would have ended casino-based gambling was overwhelmingly rejected by voters despite O’Malley’s support. And despite O’Malley’s staunch opposition, Massachusetts became a national trailblazer on same-sex marriage.

Tuesday’s event was just one part of O’Malley’s push against Ballot Question 4. The Boston Archdiocese has already sent letters to the parents of approximately 40,000 children who attend diocesan schools. A letter from the state’s four archbishops (including O’Malley) and an anti-Question 4 flier currently greet parishioners as they walk into Boston churches. Visitor’s to the Archdiocese’s Facebook page can see O’Malley urging a “No” vote. And at the annual Red Mass this past weekend, a special service for Catholic lawyers and judges, O’Malley warned of the dangers of legalization.

Asked about O’Malley’s activism, and the broader faith-based push against recreational legalization, Jim Borghesani, a spokesman for Yes on 4, said the cardinal and his allies “have it backward.” Legalization would be safer for consumers who currently purchase marijuana illegally, Borghesani said, and would end the legal disparities that currently exist.