BOSTON (SHNS) – Gov. Charlie Baker is seriously considering a veto of climate legislation that would commit Massachusetts to going carbon neutral by 2050, according to multiple sources, raising deep fears within the environmental community that the bill’s failure could send a troubling signal to other states looking to Massachusetts as a guidepost.

Baker has not yet decided what he will do, but members of his administration have told stakeholders that there is a possibility he will pocket veto the legislation by taking no action on the bill. The governor has until Thursday to act on the legislation that was passed Jan. 4, and if he doesn’t sign it the bill will simply die.

Baker, according to sources, agrees with most major elements of the legislation (S 2995), including the statewide requirement of net-zero carbon emissions by 2050 and the advancement of offshore wind. Baker set an identical emission reduction goal by executive action earlier this year.

The governor, however, has concerns with some of the interim reduction targets set by the bill, and would prefer a less prescriptive and cost-conscious approach to reducing carbon emissions than the sector-by-sector approach outlined in the legislation.

“Some grave concern setting in,” said one person familiar with the administration’s process, who requested anonymity to discuss private conversations.

An advisor to the governor said Baker was “still reviewing” the legislation.

The pressure to sign the bill is coming from many lawmakers and environmental groups, though the real estate industry and the Greater Boston Chamber of Commerce have flagged areas of concern to them as well.

U.S. Sen. Edward Markey even weighed in on Monday.

“Massachusetts has always been a pace-setter for national progress. On climate change and environmental justice, it should be no different. This bill on Governor Baker’s desk is a key opportunity for the Commonwealth to continue working for the common good,” Markey tweeted.

In addition to committing the state to net-zero emissions by 2050, the bill would establish energy efficiency standards for appliances and authorize additional purchases of offshore wind power, solidifying wind as the backbone of the state’s transition to clean energy transition.

But Baker is said to be frustrated with the Legislature that they would send him a bill with so many complex pieces so close to the end of the session, giving him few options to respond.

The governor and his team also feel they were “boxed out of the conference committee negotiation process,” despite lawmakers knowing how the lateness of the bill would tie his hands, according to someone who has spoken to officials in the administration.

At the tail end of a two-year session, House and Senate negotiators struck a deal and passed the climate bill just days before they ended their session. Now, Baker can either sign the legislation or let it die on his desk, but no longer has an opportunity to offer amendments.

One source within the environmental community said they spoke to a “heated and very frustrated” official in the administration who felt the process should have been handled differently.

“If he doesn’t sign this, the Legislature owns part of this failure,” the person said.

Sen. Michael Barrett, the lead negotiator for the Senate on the bill, told the News Service he had not spoken directly to the administration, but said, “There do seem to be grounds for concern for a veto.”

“A veto now would feel very odd and be very unfortunate. A real betrayal,” Barrett said. “It would also feel a little bit like a setup since they had time to approach us about a meeting in the middle.”

One of the issues Baker has with the bill is the 2030 emission reduction target.

While the bill calls for emissions to be 50 percent below 1990 levels by the start of the next decade, the administration’s own plan has a target of 45 percent, and Energy Secretary Kathleen Theoharides has said that anything greater would be risk being “unnecessarily disruptive to the economy and likely extremely costly, particularly for people who can least afford it.”

Barrett said that Baker had a year since last January when the Senate passed its original bill to raise those concerns, but never approached him. He said it’s no excuse that the administration only late last month published its “roadmap” to achieve net-zero emissions by 2050.

“They can walk and chew gum at the same time over there,” Barrett said.

Barrett said there were “high-level” discussions on Jan. 5 — the last day of the session that went until after 4 a.m. on Jan. 6 — about the possibility of the governor returning the bill with amendments after just a day to review the legislation, but that never happened.

Rep. Thomas Golden, the lead House negotiator, could not be reached Tuesday for comment.

Baker could choose to sign the bill, and file his own legislation to make the changes he desires, though he would be giving up any leverage he has over the Legislature if he chose that route. Barrett said he would “entertain” a bill from the governor “very respectfully.”

The level of anxiety with respect to the future of the bill reached the point Tuesday where one environmental group told the News Service conversations were already underway about what a campaign might look like to revive the bill in the new session.

“I am nervous. I think Governor Baker may not sign this and I empathize with what I imagine is his frustration with receiving this bill at the last moment. Climate change is an issue he cares a lot about,” said Environmental League of Massachusetts President Elizabeth Turnbull Henry. “It would be tragic if the timing and some of the smaller differences in policy opinion between the administration and the Legislature lead to the whole bill being scrapped.”

If Baker signs the bill into law, Massachusetts would have the most ambitious timeline for reducing carbon emissions in the country, surpassing even New York and California.

“All eyes are on Massachusetts,” said Turnbull Henry. “We would become the national leader in climate policy. This bill will motivate and inspire other states to act and I hope we send the right message to those states before Thursday.”

Stephan Roundtree, Northeast director for Vote Solar, said he still believed Baker would sign the bill. He also said the more aggressive 2030 emission target was within reach by expanding the state’s SMART program, a solar incentive program.

“They could open the throttle on solar and in the process create a lot of jobs in a lot of sectors,” Roundtree said.

Baker did not file an equivalent bill to the mash-up that landed on his desk, though he did declare his support for going carbon neutral by 2050 in his State of the Commonwealth address last January.

Instead, Baker last session proposed to raise $1 billion over the next decade by increasing the real estate transfer tax to invest in climate change mitigation projects. The higher tax would have raised $137 million a year. Former House Speaker Robert DeLeo responded with his own “Green Works” bill to instead borrow more than a billion dollars over the next 10 years, but neither proposal gained traction in the Senate.

Without straight-up asking the governor to veto the bill, Greater Boston Chamber of Commerce CEO Jim Rooney last week wrote a letter to Secretary Theoharides asking the administration to “carefully consider” the short-term and long-term impact of a municipal opt-in stretch energy code for new construction.

Rooney said that even while “well-intended” the stretch energy code provision would create a patchwork of building codes around the state.

“Where technologically feasible, constructing net-zero buildings is costly and sometimes cost prohibitive. Whether it is commercial or residential construction, the costs of implementing this provision will immediately be passed along to buyers and renters, threatening to exacerbate our housing crisis and undermine our economic recovery,” Rooney wrote.