A state judge has temporarily blocked the Parks and Recreation Department from continuing its $21 million overhaul of the north end of Union Square Park.
The project, which includes installing a new restaurant in the park’s pavilion, has been opposed by various neighborhood groups, which say the establishment of a privately owned restaurant would be an illegal use of public parkland.
A temporary restraining order, issued Monday afternoon by Justice John E. H. Stackhouse of State Supreme Court in Manhattan, prohibits the city “from engaging in any physical destruction, site preparation and/or construction” relating to the renovation.
The judge’s order was issued in response to a lawsuit filed by Geoffrey Croft, president of NYC Park Advocates; the Union Square Park Community Coalition, a neighborhood group; Carol Greitzer, a former councilwoman; and others.
Justice Stackhouse set a hearing for Monday to determine whether to issue a preliminary injunction, which would prevent the parks department from performing work in the park for a longer period.
Workers started site work at the park several days ago. On Tuesday, hours after the restraining order was issued, a backhoe sat idle in the park’s north plaza, its arm resting atop a large mound of dirt. Equipment from two of the park’s three playgrounds had already been removed.
A parks department spokeswoman declined to comment on Tuesday.
But in a statement, Ramin Pejan, a lawyer at the city’s Law Department, said that the Bloomberg administration would eventually prevail.
“The city is confident in its legal position and the merits of this project, which include a redesigned and dramatically expanded playground and a rehabilitated historic pavilion and plaza that was supported by the community board and approved by the Art Commission,” Mr. Pejan said.
The dispute over Union Square, one of the city’s most popular public spaces, is the latest in a series of disagreements between the parks department and neighborhood groups over changes to local parks that have ended in lawsuits and protracted court battles.
In January, ruling on a lawsuit by community groups, Justice Shirley Kornreich of State Supreme Court in Manhattan ordered the department to void a $45 million deal between the agency and 20 private schools to build sports fields on Randalls Island, at the confluence of the East and Harlem Rivers.
Justice Kornreich determined that the department had failed to properly follow city and state competitive-bidding and public-review rules.
At Union Square Park, proposed changes include the new restaurant, the redesign of two playgrounds and the repaving of asphalt where a popular greenmarket has been situated for several years. The plan also calls for about 14 trees to be cut down.
The work had been scheduled to be completed before the end of next year, according to the parks department’s Web site.
The Union Square lawsuit maintains that the city failed to get the approval of the State Legislature before deciding to place a restaurant in the park.
State law requires that when the public use of a park or section of park is changed to a nonpark use, the change must be approved by state government.
On Tuesday, opponents of the redesign said the judge’s decision was a first step.
“The temporary restraining order is a small but important step in the right direction,” said Assemblyman Richard N. Gottfried, whose district borders Union Square. “They are taking away a piece of the park. You wouldn’t use the park for a bookstore or a shoe shop, and you shouldn’t use it for a restaurant.”
Mr. Croft said the Union Square area, which has become home to many young families in recent years, needs more playgrounds for children.
“The city is taking away thousands of square feet of potential play space in an area with the lowest amount of play space in the city and one of the highest concentration of restaurants,” he said.
