In the latest turn in the fight over a proposed new $60 million, 950-student middle school in Clifton Heights, the Upper Darby school board voted, 8-0, Monday night to break the borough’s lease on the proposed construction site and begin seeking permits for a project that is opposed by many residents.

The emergency vote is likely to escalate tensions between residents of Clifton Heights, who say they’re fighting to preserve the last open space in their 6,500-person borough, and school leaders, who say that Upper Darby desperately needs a third middle school to fix classroom overcrowding and that the contested site makes the most sense.

“Our buildings are overcrowded and have been for too long,” board president Rachel Mitchell said in a statement ahead of the unanimous vote, adding that the move came after a lengthy and thorough planning process.

Last week, Clifton Heights advertised proposed major changes in its zoning ordinance that could either prevent or at least slow down the push for the new school. The changes — which included new requirements for environmental and traffic impact statements — were set for a May 28 vote.

In response, the Upper Darby school board called Monday night’s emergency meeting to vote on terminating the borough’s $1-a-year lease on the property, which dates to the 1970s. Officials said the vote would start the clock on the project — slated for completion in 2023 — and render any subsequent zoning changes moot.

The resolution approved on Monday night also authorized the district’s architects and engineers to submit planning documents to the borough and to Delaware County. It set an Aug. 6 termination date for the lease unless an agreement can be worked out sooner.

Last Thursday, the borough’s solicitor, Francis J. Catania, sent a letter to the school board calling the lease termination “vindictive” and threatening legal action in response.

Board members in Delaware County’s largest school district had been poised to vote last month to cancel the lease but postponed the move, two nights after an estimated 500 Clifton Heights residents staged a protest on the field.

Borough residents say they are afraid the 150,000-square-foot school would destroy a popular gathering spot for community events such as Police Athletic League sports, Fourth of July fireworks, and the Boys Club’s annual Cow Pie Bingo.

Clifton Heights Mayor Joseph Lombardo has vowed that the borough “would do everything in our power to save our fields” and also threatened legal action, even as he insisted the proposed zoning changes had been in the works before the school plan was even announced.

Upper Darby officials say that plan to reach agreements with community groups to use ball fields and the gym at the new school.