Representatives from labor unions, colleges and the business community were among those who spoke against the so called "shadow bill" meant to protect sunlight in public parks, saying it would wind up prohibiting development in the city during a legislative hearing Tuesday at the State House.

"Bill H.1169 would effectively kill most development in the central city for the foreseeable future," said Stuart Street resident Greg Selkoe, a board member of the Emerald Necklace Conservancy.

Legislators did not vote during the hearing Tuesday morning at the State House, and the bill is pending in the Joint Committee on Environment, Natural Resources and Agriculture.

Proposed by Reps. Marty Walz and Byron Rushing, the bill would prohibit shadows cast on parks by new buildings that are constructed at a height above what's allowed under the existing zoning laws.

Supported by the Neighborhood Associaiton of the Back Bay, and many residents who agree the parks need to be protected, it's about preserving the open space and fresh air that people living in the city have come to depend on, said Rep. Walz.

"This is not some new scheme that we dreamed up to stop development," Walz said. "Why would we do that to our city?"

But the problem, said Meg Mainzer-Cohen, president of the Back Bay Association, is developers get variances all the time. That special approval process to build higher than existing zoning laws exists for a reason, and often makes a project worth while.

If developers can't build up because of shadows, projects won't move forward, and it will result in the loss of jobs, housing units, and real estate taxes to the city, she said.

"This bill will essentially prohibit smart growth in Boston," Mainzer Cohen said.

Packed into a room at the State House, those opposed referred to it as "sweeping legislation" that should be, and currently is, managed on a local level with every project scrutinized on a case by case basis. They also took issue with restrictive language that wouldn't allow a new building casting, say, a five foot shadow on Copley Square for 10 minutes in the middle of December.

"I'm not so sure the new MFA wing could have been built adjacent to the Fenway had this legislation been in place," said Ronald Druker of the Druker Company.

The parks included in the proposal are the Charles River Esplanade, Christopher Columbus Park, Commonwealth Avenue Mall, Copley Square Park, Magazine Beach Park in Cambridge, and Back Bay Fens.

The Boston Common and Public Garden are already protected by legislation passed in 1990 and 1992, respectively. "Despite dire predictions of economic harm" the city has still seen growth in these areas, said a letter from the Neighborhood Association. Adding these other parks to the list will ensure they remain bright, friendly public places - especially as high-rises, like the Liberty Mutual Tower and Copley Place expansion - go up around them, proponents said.

"Numerous high-rise projects are being proposed along the High Spine between Downtown and the Fenway, and we feel that our parks are not adequately protected," said a letter from the Neighborhood Association. "Parks that are in perpetual shadow are cold, unwelcoming and less likely to be enjoyed, becoming a detriment to the city rather than remaining the attractive asset they are today."

But the Boston Redevlopment Authority has an extensive approval process that includes studies of wind, light and shadow for new projects. The city carfully analyzes every new development, so the tools are already in place to make sure they don't block out the sun, those opposed to the bill said.

"Name a project that has cast a shadow longer than an hour on a park," Mainzer-Cohen said after the meeting.

Yet as density increases, once the sunlight is gone it's not coming back, supporters said.

"This bill allows and encourages reasonably scaled development near our parks, while protecting sufficient sunlight for the health of the park and the enjoyment of its users," Prindle said. "This is the balance that will make a healthy and thriving city."