The Williston-West Church on Thomas Street in Portland’s upscale West End is at the center of a development controversy.

PORTLAND — A group of 12 Portland residents has filed a lawsuit to prevent wealthy Australian developer Frank Monsour from renovating the historic Williston-West Church complex for office space.

The superior court filing is the latest blow in a battle over the late 19th century church and accompanying parish house, which Monsour reportedly hopes to convert in part to an American home base for his mobile data systems company Majella Global Technologies.

Some neighbors of the 32 Thomas St. site opposed the project during a series of planning board and City Council workshops and meetings in April, May and June, arguing the allowance of offices in the otherwise densely residential part of town would be a change for the worse for the neighborhood.

But the council approved the plan by a 6-3 vote last month, with the majority of councilors agreeing that opening the door to offices at the West End site is necessary to encourage investment in preserving the aging property.

Now, many of the residents who fought the project through the municipal meetings are taking the battle a step further, asking the court to step in and throw out the city rezone.

“We’re just asking the court to review what the city did, and to be clear whether it’s valid or not,” said Bruce McLauflin of the Portland law firm Petruccelli, Martin & Haddow, who is representing 11 of the 12 plaintiffs in the case. “The permitted uses in that zone are all residential. The question is, did the city take contract zoning further than what the Legislature intended … when it authorized municipalities to use contract zoning.”

Monsour, doing business locally as 32 Thomas Street LLC, is proposing to convert the parish house into a personal residence and company offices to accommodate no more than 14 employees, with the church’s sanctuary space initially envisioned as a community hall or performing arts venue.

Lining up as plaintiffs in superior court against the project are Charles and Kathy Remmel, John and Betty Gundersdorf, Samuel and Judith D’Amico, Jerry W. West and Diane Worthington, Judith Mansing and Sid Tripp, and Judy and Orlando E. Delogu. Orland Delogu is a former Portland City Councilor and University of Maine School of Law professor and is representing himself in the case.

The plaintiffs are suing not only 32 Thomas Street LLC but the city of Portland as well. Preserving historic structures is a priority in the city’s comprehensive plan, a point central to the project’s approval, but opponents say that’s not enough to override the zoning restrictions on commercial office space in the area.

“People buy [homes in] a zone knowing what the permitted and nonpermitted uses are. They rely on that in making their decisions, and then all of a sudden certain individuals show up and say, ‘Well, I don’t like what the permitted and nonpermitted uses are,’ and go to the city to change them,” McLauflin said Tuesday.

Portland city attorney Danielle West-Chuhta said she’s “confident the court will agree” with the City Council’s decision on the topic.

“The City Council and the Planning Board gave the applicant — as well as the public — a full and fair hearing, looked at all the arguments listed in this complaint, and based on a thorough and thick record, decided this is in agreement with the comprehensive plan and the neighborhood, which is what the law requires,” she said.

Mary Costigan, an attorney with the Portland law firm Bernstein Shur representing Monsour, told the BDN on Tuesday her “client will have some decisions to make” on whether to delay work on the project while the court process plays out.

But she said she believes the contract zoning will hold up in superior court, a perspective shared by Jed Rathband, a former Portland mayoral candidate who works as a local consultant to Monsour.

“It’s unfortunate these neighbors have resorted to this, but I don’t think they have much of case,” Rathband said. “In contrast, there is a good number of people within the neighborhood who support this and would like to see this project move on. We had support all across the city, we had support on the city council, and that support has only grown throughout the process.”