Lansing — Gov. Rick Snyder will decide the fate of a controversial plan that would give the Republican-led Legislature greater power to intervene in state legal battles next year when Democratic Attorney General-elect Dana Nessel takes office.

The lame-duck legislation approved late Thursday in an overnight session seeks to guarantee that the Michigan House or Senate could join any court case challenging the constitutionality or validity of a state law or any action by the Legislature.

Nessel, who will be sworn in Jan. 1 as the first Democratic attorney general in 16 years, "is deeply concerned and troubled" by the measure, said transitional spokeswoman Kelly Rossman-McKinney.

She called it a rushed effort "to push through a proposal that was never properly vetted and appears to be an intentional and partisan effort on the part of some legislators to undermine the role of the state's attorney general."

The bill is among a handful of late-year Republican proposals that have sparked Capitol protests and garnered national attention.

The House this week effectively killed a controversial Senate bill that would have shifted campaign finance oversight away from Democratic Secretary of State-elect Jocelyn Benson. But GOP lawmakers sent Snyder other proposals that would make petition drives more difficult and shield donors to nonprofit political groups from inquiries by Benson, Nessel or other government officials.

The term-limited governor is considered a wild card on signing the court intervention legislation. Unlike GOP Gov. Scott Walker in Wisconsin, Snyder has given lawmakers no indication he’ll sign measures that would strip power from Democrats set to take over top statewide offices next year — a stance that may have contributed to the demise of the campaign finance shift bill.

Snyder sent lawmakers a signal Friday when he vetoed legislation that would have given the auditor general — an independent arm of the Legislature — the power to access confidential information in each branch of state government.

"As governor, I have an important obligation to protect one of the fundamental principles of our constitution — the separation of power," he wrote in his veto letter.

Snyder ignored protests when he recently signed controversial lame-duck measures weakening paid sick leave and minimum wage initiatives after legislative Republicans pared back some more dramatic cuts at his suggestion. The two amended initiated laws are likely to face court challenges.

“I look at legislation presented to me through a policy lens — is it the right policy for the state of Michigan and Michiganders as a whole? That’s what I did with these bills and have now signed them into law,” Snyder said last week as he signed the sick leave and minimum wage measures.

Sponsoring Rep. Rob VerHeulen, R-Walker, has bemoaned comparisons between his court intervention legislation and other controversial bills in Michigan or other states that would limit the power of incoming Democrats.

“There are times where the attorney general may not be the appropriate spokesperson for the House or Senate,” VerHeulen said last week. “They may have a sincerely held belief the position taken by the House or Senate is not constitutional.”

Former Attorney General Frank Kelley, a Democrat who held the post for 37 years, is among those calling on Snyder to veto the measure, saying it would be "an appalling abuse of power by the governor to sign the intervention bill."

"The Legislature was created through the Constitution to make laws as to how the state shall be governed," Kelley said in a statement. "No state legislative body has ever been allowed to conduct the affairs of government. The Legislature gives that power to the state agencies that actually operate the government."

The Republican-led Senate approved the intervention bill in a 26-12 vote, and the GOP-led House sent it to Snyder's desk in a 60-47 concurrence vote.

Nessel said during her campaign she may not defend state laws she views as unconstitutional, including a 2015 law that allows faith-based adoption agencies to decline working with gay residents. Same-sex couples have sued the state over the law, and the litigation remains in court.

“Let’s be clear, the attorney general-elect has already said there are certain things she’s not going to defend and there’s other places she’s going to intervene,” Senate Majority Leader Arlan Meekhof, R-West Olive, said last week. “By all means, we should have the priority status to defend the stuff that we’ve done, and I think that is important.”

Republicans have also insisted the bill is at least partially a response to recent conflicts. The Michigan auditor general, which is the independent oversight of the Legislature, in January took the rare step of suing the Snyder administration, which is represented by the attorney general, after the state Department of Health and Human Services declined to hand over requested records.

Legislative Democrats opposed the court intervention plan, which Sen. Steve Bieda of Warren argued was among a series of “hastily written and borderline unconstitutional" bills pushed through in the the lame-duck session.

Constitutional authors who spelled out separation of powers between governmental branches are “rolling in their graves right now,” Bieda said. “If you’re worried about a law you passed being challenged in court, there’s one simple solution: Write better legislation.”

The House or Senate already can ask a court to intervene in state court cases, but the proposal would guarantee that ability, which is a power typically reserved for the attorney general. Judges have occasionally rejected the Legislature's request to intervene.

Under the proposal, the House or Senate could prosecute an appeal, apply for a rehearing or take other steps allowed by the primary parties in a case, including Nessel or Democratic Gov.-elect Gretchen Whitmer.

Snyder has repeatedly declined to weigh in on the legislative intervention bill or other lame-duck measures until they reach his desk. But the term-limited governor said last week he is "not a horse trader" and told reporters he'll review each bill to determine "is it good for the people of Michigan or not."

Legislators who voted for the court intervention plan "would be wise to remember that the people elect their attorneys general and their governors and this legislation ... will have dramatic and disastrous impact on the state of Michigan and its residents for years to come," said Nessel's spokeswoman. "The attorney general-elect stands in opposition to this legislation."

joosting@detroitnews.com