The dispute has threatened to pit two unions against each other. Morton Williams employees are represented by the Retail, Wholesale and Department Store Union. Dozens of members showed up last week to hear Richard L. Trumka, the newly elected president of the A.F.L.-C.I.O., praise the Kingsbridge alliance as a model community involvement. At a rally in front of the armory, Mr. Trumka said the building could either become the heart of the surrounding area or it could become “a profit center for people outside the community.”

Large supermarkets in the New York area are represented by the United Food and Commercial Workers Union Local 1500, however. Pat Purcell, director of special projects for the local, said an operator like Pathmark could bring in hundreds of union jobs. “If we knew it was a unionized employer, it would be very difficult for us not to be supportive,” he said.

According to recent census data, 28 percent of Bronx residents live in poverty, making it the poorest urban county in the nation. The August unemployment rate was 13.2 percent.

In recent years, community benefits agreements have eased the way for numerous large projects in New York and elsewhere. Wage and local hiring guarantees have been a standard part of such pacts, and many have also included a ban on big-box stores or pawnshops and checking-cashing stores. In the agreement for its newly opened Gateway Center at Bronx Terminal Market, Related agreed not to lease space to Wal-Mart. Some contracts have enumerated preferred retail uses.

Amy Lavine, a staff lawyer at the Government Law Center at Albany Law School, who monitors community benefits agreements, said she knew of no other pact that excluded supermarkets and grocery stores. “Completely excluding a use that’s beneficial to a community (as opposed to pawnshops and the like) may be counterproductive and not in the community’s best interests,” she said. While protecting existing businesses may be a worthy goal, she said, “protecting specific individual stores raises a perception of favoritism and verges on being anticompetitive.”

Image Valerie Sloan is a vice president of Morton Williams Supermarkets. Credit... Richard Perry/The New York Times

But John Goldstein, the national program director for the Partnership for Working Families, which provides technical assistance to local organizations, including the Kingsbridge alliance, said it was important to protect local businesses that were willing to invest in a low-income community when other businesses would not.