PHILADELPHIA -- In a jab at state gaming officials, City Council voted unanimously Thursday to place a referendum on the spring primary ballot that, if passed, could seriously hamper plans for two casinos along Philadelphia's waterfront.

Members voted 17-0 in favor of asking voters in the May 15 primary whether the city charter should be amended to ban the building of casinos within 1,500 feet of homes, churches and schools. The decision brought simultaneous cheers and boos from hundreds of casino opponents and supporters who were part of a standing-room-only crowd in council chambers.

It also brought swift reaction from the Pennsylvania Gaming Control Board, which gave SugarHouse and Foxwoods approval in December to build along the Delaware River in Philadelphia.

Tad Decker, the gaming board's chairman, said the agency will challenge the legality of the ballot question because it contradicts the state law that legalized slot machines and authorized two casinos in Philadelphia.

"It's clearly a violation of the gaming act," Mr. Decker told reporters after the board's public meeting in Harrisburg. "They're not allowed to pass it."

The agency likely will ask the state Supreme Court to take the case and prevent the Philadelphia city clerk from authorizing the question for the ballot, Mr. Decker said.

Gov. Ed Rendell's communications director, Doug Rohanna, said City Council's vote raises fundamental constitutional questions. But he could not say immediately whether the administration, which has championed slot machines, would challenge the vote in court.

The referendum, if approved, could force the gaming board to start the licensing process all over again since the locations were crucial to winning the slots licenses.

"If the site fails, then I would expect that others would say we have to pick a new site," said Bob Krauss, a Philadelphia lawyer who is vice chairman of the Pennsylvania Bar Association's gaming law committee. "We have to let everybody reapply."

SugarHouse plans to build a slots casino just north of the Ben Franklin Bridge, in Fishtown, while Foxwoods has chosen a site less than two miles away in South Philadelphia.

If these sites are banned, the casinos will be left with less desirable locations to build, possibly even causing them to rethink plans to open.

Philadelphia Councilman Frank DiCicco said the city is left without much choice but to challenge the state's slots law, passed in the wee hours of a holiday weekend in July 2004. He said the public has the right to be heard and that council members should support the democratic process.

"We are the last line of defense," said Mr. DiCicco, in an impassioned plea before his peers. "This is a matter that will affect the city of Philadelphia for decades to come."

SugarHouse spokesman Dan Fee said there will be a high price to pay if casino plans are thwarted.

"Today's vote is a vote against thousands of new jobs, millions of dollars for our schools and tax cuts for everyone who lives and works in Philadelphia," he said. "We're obviously disappointed."

Foxwoods said in a statement that the vote "sends a message to business that Philadelphia is not a city that welcomes positive economic development."

In contrast, Anne Dicker, an organizer for Casino Free Philadelphia, was elated.

"I'm very happy," she said. "This is our first victory."

Last week, a judge invalidated a petition the anti-casino group submitted to the city in an effort to get the same referendum on the ballot. The council's unanimous vote to approve the ballot question made the petition issue moot.

Council members took the vote Thursday despite a warning from City Solicitor Romulo L. Diaz Jr. that even if voters approve the referendum, it would only delay the casinos. The state, not the city, has the authority to choose slots locations, he said.

A constitutional law professor at Temple University said the case would set up an interesting clash between the slots law and Philadelphia's home rule authority under the state constitution.

The state Supreme Court has tended to side with the Legislature on other home rule issues, such as gun laws, said professor David Kairys.

"You can only make predictions; there's no certain answer to this," Kairys said. "But I would say that the way the Supreme Court has been going, it would probably rule against the interests in the city that want to limit gambling, or eliminate it."

The Mashantucket Pequot Tribal Nation, which runs the huge Foxwoods Resort Casino on its Connecticut reservation, is the biggest investor in Foxwoods Casino Philadelphia. Chicago's billionaire developer Neil G. Bluhm is the biggest investor in SugarHouse.