A plan to shrink Illinois’ carbon footprint and steer hundreds of millions of dollars in ratepayer subsidies to Exelon failed to materialize in Springfield Tuesday amid feuding between environmentalists and organized labor, leaving one of Gov. JB Pritzker’s key priorities in doubt.

The Illinois Senate had convened Tuesday to take up a green energy package that was a big piece of unfinished business from the spring legislative session that could have broad ramifications.

But Senate President Don Harmon, D-Oak Park, said no deal came together, largely due to concerns about phasing out natural gas-fueled power plants before mid-century — an integral part of Pritzker’s plan to reduce greenhouse gas emissions in Illinois and a top aim for environmental groups.

That priority ran headlong into the potential loss of thousands of union jobs at those facilities, leaving labor unwilling to sign on to an energy deal and forcing Senate Democrats to choose sides between two influential blocs within the party, Harmon said.

“We don’t want to vote for something that puts us in the middle of a fight between friends, between key constituencies, between organized labor and the environmental community,” Senate President Don Harmon, D-Oak Park, said at a press briefing after the Senate shut down without an energy vote Tuesday night.

“There is a deal to be reached, and we just need to get them back at the table and push a little bit harder,” he said. “I’m confident we’ll be able to do that.”

There is no timetable for Harmon’s legislative chamber to return to Springfield, but the inaction could trigger Exelon to ratchet up plans to mothball its financially ailing nuclear plants at Byron and Dresden and imperil union jobs at those facilities.

Under a deal Pritzker’s office brokered and that was to be part of the energy package, Exelon was in line to get $694 million in new ratepayer subsidies in exchange for keeping those two plants and one at Braidwood open for another five years.

“We are disappointed that a comprehensive climate and energy bill that would preserve Illinois’ largest source of clean energy failed to pass, paradoxically putting at risk the clean air and jobs goals that all policymakers rightfully agree are critical to our state,” Exelon spokesman Paul Adams said in a statement Tuesday evening.

“We are mindful and appreciative of efforts by environmentalists and labor leaders to continue negotiating on the remaining issues, and we hope that legislative leaders are right in expressing optimism that this stalemate may be resolved in time to preserve Illinois’ nuclear fleet,” Adams said. “Absent quick passage of legislation, Exelon has no choice but to proceed with retiring Byron in September and Dresden in November, as previously announced.”

Pritzker’s administration had tried to mollify concerns within Harmon’s caucus about the fate of coal-burning plants in Springfield and the high-polluting Prairie State Energy Campus in far downstate Marissa by extending their lifespans to 2045 so long as they were able to contain 90% of their carbon emissions. The governor had earlier advocated for the plants’ closure by 2035.

But that concession didn’t do anything to jump-start the legislative inertia surrounding the energy package, leaving aides to the governor disappointed and frustrated with the day’s developments.

“The governor’s office [Tuesday] presented a comprehensive, compromise energy package,” said Deputy Gov. Christian Mitchell, Pritzker’s point man on energy talks. “That package doubled our commitment to renewable energy, put us on a path of 100%clean power by 2050, would have allowed an exemption for Prairie State and [Springfield] if they reached 90% carbon capture by 2034 to stay open til 2045, provided a rightsized subsidy to Exelon to preserve their nuclear fleet and would have made Illinois the best place in the country to make or manufacture an electric car, and all of that leading with ethics.

“The Senate chose not to take up that bill today,” Mitchell said.

But Republicans pinned blame for the inaction on Pritzker himself.

“Unfortunately, the governor’s unrealistic demands in his bill, proposals that would cost thousands of jobs and potentially increase our electric bills up to 20%, were the reason the Illinois Senate did not take a vote on any energy legislation,” said state Sen. Sue Rezin, R-Morris, whose legislative district includes three Exelon plants.

“There simply was not enough support for the governor’s plan, and he was not willing to negotiate with the unions,” she said.

Meanwhile, the state House of Representatives is scheduled to meet Wednesday. It’s expected to take up a measure that would let Chicago voters elect a public school board. The plan faces opposition from Mayor Lori Lightfoot, who currently has the power to appoint all members of the Chicago Board of Education, which governs the city’s schools.

Dave McKinney and Tony Arnold cover Illinois politics and government for WBEZ. Follow them on Twitter @davemckinney and @tonyjarnold.