The downside of Boston’s building boom could be a parking crunch as a series of massive construction projects gets underway, business and community leaders are warning, while Mayor Martin J. Walsh is banking on MBTA improvements and alternative modes of transport.

“Parking is huge issue all over the city,” said Sue Sullivan of the Newmarket Business Association, who said she worries that proposed mega-projects such as the $1.5 billion Government Center Garage redevelopment and the rapid expansion of the Seaport District, where General Electric will soon move its global headquarters, will have a ripple effect on parking throughout the city if cars are pushed out of those areas.

“Construction itself causes disruptions and I don’t know how you mitigate that,” Sullivan added. “You have to get the construction done and they say after they’re finished there’ll be parking — but during that time they have to figure something out.”

Evan Falchuk of the United Independent Party said more has to be done before major construction projects are given the green light.

“It’s going to be a disaster if there isn’t a bigger plan in place,” Falchuk said. “It’s not just Government Center, with everything happening in the Seaport, we’re in a really exciting boom time — but we don’t seem to be great at the kind of comprehensive planning that’s needed to make sure it’s not just, ‘We’re tearing down a garage, we should figure out a way to find spaces.’ ”

Jon Hurst of the Retailers Association of Massachusetts said, “No issue is more important to downtown merchants … parking is vital. You’ve got to have adequate parking at reasonable prices. I know there are some planners that want to cut down on cars, want to see them all use public transportation and so forth, but consumers have unlimited options today for where they spend their money and if we make it too difficult or too costly for them they’re not going to spend it where you are.”

Tom O’Brien of HYM Investment Group, redevelopers of the Government Center Garage, said that facility is usually only half full — and HYM plans to keep half of the 2,500 spaces.

Walsh spokeswoman Bonnie McGilpin said in a statement City Hall is “currently reviewing the impact of these new developments on parking” and the mayor has directed the Boston Transportation Department to “focus on mobility options through Go Boston 2030,” an initiative aimed at planning Boston’s transportation future.

“This includes our Drive Boston partnership to ?encourage car sharing, expansion of Boston Bikes, and working with the MBTA to create a dependable public transportation system for residents and visitors,” she said. “We are focused on making our transportation system more data driven so we can better inform customers of transportation options, so that they can make informed decisions about how they want to get around the city.”