It was only a few weeks ago that Mayor Marty Walsh made it clear that he was ambivalent about a proposal by several Council members to raise the city’s property tax by about one percent in order to trigger matching state funds for community preservation, a concept that promotes affordable housing.

The proposal would cost the average owner-occupied single-family house about $28 extra per year, and would raise an estimated $13-14 million from city residents and a matching $5-6 million from the state in funds set aside by the Community Preservation Act, or CPA.

If approved by the Council and the mayor, the measure would be put on the November ballot for city residents to decide. A similar proposal failed in 2001; but that ballot measure called for a 2% property tax increase.

It was City Council members, not the mayor — principally at-large member Michael Flaherty and District 4 Councilor Andrea Joy Campbell — who first floated the idea about a month ago, arguing that Boston was leaving “money on the table,” as Flaherty put it at a hearing on the bill, by not opting into the program.

Members of the Walsh administration who attended the hearing were noticeably vague about the administration’s position on the measure, noting repeatedly their “interest.”

And when Walsh unveiled his budget proposal to Council members and the press a week later, he did hide his reluctance to support CPA, telling Council members and the press:

“Right now, the CPA match is a thirty percent match, not a hundred percent match, and if Boston jumps in … the match is probably going to go probably from 30% to 20% so we’re not even going to get the investment CPA talks about.”

The mayor also cited Boston’s disproportionate reliance on property tax revenue, suggesting that raising property taxes only added to the imbalance and to the potential vulnerability of Boston to the real estate market.

Today, however, Walsh declared his administration to be “all in” supporting the CPA ballot measure.

Flanked by the bill’s sponsors in Council, members of his administration, and representatives from the Greater Boston Interfaith Organization, which has lobbied hard for CPA, Walsh said that the extra funds would help longtime Bostonians stay in ever-more-expensive neighborhoods.

“We believe it offers a offers a balanced and timely strategy for helping us build affordable housing, invest our parks, and preserve Boston’s historic and inclusive character.”

“Success has brought challenges,” Walsh added, “housing being one of the greatest.”

Asked by a reporter why the mayor had changed his mind, he gestured at the cheering crowd, many in Greater Boston Interfaith Organization tee shirts.

“Do you see these shirts that are around you right now?” the mayor asked rhetorically. “Advocacy.”

Jamaada Smith, speaking on behalf of GBIO, said that she's seen her own religious community shrink as members of her church purchase houses — outside of the city. 

"We support CPA, because it is one defined step in the direction of affordable housing," Smith said. 

Walsh acknowledged potential push-back, especially from the business community.

As to whether Boston voters will come around this time, Walsh said he was optimistic and that he would actively advocate for ballot approval of CPA. "We’re not in this to lose the ballot question in November,” said the mayor. “If that was the case then I wouldn’t be standing in front of City Hall today.”