Wu says 70% of Boston's greenhouse gas emissions come from the buildings sector. “This new green building code will help ensure that we set the foundation for healthy, resilient growth throughout our neighborhoods,” Wu said in a statement when she announced the plan last month.

Wu’s signature at a special event on April 13 at the Museum of Science followed an 8-4 vote the previous week by the Boston City Council to adopt the new state “specialized code,” which added requirements to the state’s already stringent “stretch” energy building code.

The new rules will go into effect in Boston on Jan. 1, giving developers and other builders eight months to get proposed projects approved and into construction, if they want to stay under the old energy code.

Some say the new requirements come at an inopportune time, with developers already struggling to keep planned projects moving forward amid the big jump in interest rates, sky-high construction costs and a pullback by banks from lending on new developments.

“It just makes things that much more difficult to move forward with projects,” says Ted Tye, managing director of National Development, which has built a number of major residential projects in Boston and its suburbs, including the Ink Block condo and apartment complex in the South End, where the old Boston Herald building once stood.

Being forced to add additional wiring and panels will add cost, says Greg Vasil, head of the Greater Boston Real Estate Board.

Vasil says the new requirements are piled on top of the Wu administration's initiatives to hike the “linkage fees” on new lab developments and significantly boost the percentage of affordable apartments developers are required to rent out or sell at below-market rates.

“We have a lot of members who are rethinking their commitment and whether they want to build in the city anymore,” Vasil says. A number of developers with “plans still on the drawing boards” have thought long and hard about ‘do we do this or do we not do this and go to the suburbs,’” he adds.

Both the New England Gas Workers Alliance (NEGWA), an umbrella organization of United Steelworker (USW) local unions, and the United Association of Plumbers, Pipefitters and Sprinkler-fitters of Massachusetts, say they are worried the new energy regulations could pose a looming threat to the livelihoods of thousands of their members.

The unions also argue the Wu administration’s adoption of the stringent new energy regs will boost both the cost of building new housing in Boston and energy costs for renters and homeowners.

“Massachusetts has long endured an affordable housing crisis,” writes Steve Finnigan, subdistrict director for the United Steelworkers and Kathy Laflash, president of the New England Gas Workers Alliance Inc., in a letter to Boston city councilors. “The cost of housing production continues to soar, pricing many families in the Commonwealth out of home ownership.

"The additional requirements on fossil fuel connections in this proposal, including solar and electrification provisions, will stifle the transit-oriented development that promises to alleviate some of our housing shortages," they say. "Housing production will suffer.”

“One of the things I have been battling is straight out bans on fossil fuels,” said Harry Brett, international representative of the United Association of Plumbers, Pipefitters and Sprinkler-fitters of Massachusetts. “It’s hard to argue with people trying to save the planet. We all agree we need to decarbonize. It should be more about plans and how to get to decarbonization.”