OLYMPIA — When Gov. Jay Inslee vetoed a 12-word sentence in the transportation budget in May, he knew what he was doing was without precedent in this state.

Now, lawmakers are gearing up to sue the Democratic governor because they think it was not just unprecedented, it was illegal.

Since Inslee acted May 21, attorneys for the Democratic and Republican caucuses have been researching whether the two-term governor crossed a constitutional line separating his veto authority from their legislating turf.

Leaders in each of the four caucuses have called the veto “troubling” and “concerning.” They set out months ago to get a legal analysis — essentially building a case. As of Aug. 28, they had not said if they would take on Inslee, who in the past two weeks ended his bid for president and embarked on a campaign for a third term.

While overriding his veto is an option, that would mean waiting until the start of the 2020 session in January and lawmakers have sounded of late like they want to do something sooner.

Democrats, who control majorities in both chambers, have been more guarded in their comments on what they want to do and when. Republican lawmakers have been more vocal in desiring to see the Legislature push back.

“It’s wrong and that’s why we’ve got to sort out our best option,” said Senate Minority Leader Mark Schoesler, R-Ritzville, in early August. “It isn’t about the substance [of the sentence]. It is about other issues that could come up in the future. I think that’s what concerns lawmakers on both sides of the aisle. Whose ox gets gored next time and what budget language do you have to write so it doesn’t happen again.”

This brewing legal battle centers on one sentence that appears at the end of six provisions of the transportation budget pertaining to grant funding for transit services including purchases of buses and vanpools.

Under Inslee, laws have been passed pushing transit providers — public and private nonprofit — to move from gasoline-powered vehicles to zero-emission vehicles such as ones powered by electricity. State law lists energy efficiency standards as one of the criteria to be considered as part of the grant selection process.

In the budget, lawmakers included the line, “Fuel type may not be a factor in the grant selection process.” They said this would ensure transit agencies that are unable to make the transition to zero-emission vehicles right away are not shut out from getting some of the roughly $200 million in grants offered through the state’s public transportation program.

That line is what got cut. Inslee argued at the time of the veto that it amended existing law by changing the rules for the grant selection process. He contended the constitution requires such a revision be done with a separate bill and not through the budget.

“It’s fair to say that there is no known legal precedent in Washington that specifically authorizes a veto of a single sentence,” said Tara Lee, a spokeswoman for the governor. “But this is a very unique situation that we do not believe the courts have considered in the past. By inserting this sentence in subsections, the Legislature put the governor in the position of choosing between vetoing critical, significant transit funding and leaving his agency and others in the position of having to choose which law to violate [because the sentence conflicts with existing state law].”

If a lawsuit is filed, it won’t surprise Inslee and his staff.

Nor will it be the first go-round in court on the extent of a governor’s veto power.

In 1977, the state Supreme Court found Gov. Dan Evans went too far when the manner in which he vetoed provisions of the Residential Landlord-Tenant Act effectively rewrote the bill. In that case, the suit was brought by an association of apartment owners.

The Legislature sued Gov. Mike Lowry about the way he vetoed some budget provisions in 1994 and lawmakers sued Gov. Gary Locke over his use of the red pen on portions of a bill in 1997.

In both cases, justices said a single sentence might be a line too far.

“The budget provisos to which the Governor’s line-item veto extends include full provisos to an appropriations bill, that is, full subsections of the section of an appropriations bill,” justices wrote to Lowry. “We do not believe an “appropriations item” may be a sentence, phrase, letter, digit or anything less than the whole proviso.”

The court said you can’t veto lines or words to fundamentally change what the Legislature did, said Phil Talmadge, who served on the Supreme Court for both cases.

“It really has been decided,” he said, adding that he was not familiar with every particular in this case.

Inslee’s action grabbed Jason Mercier’s attention in May. Since then the government reform specialist for the Washington Policy Center has been waiting to see what lawmakers might do.

“The constitution is clear that the only options for vetoes are sectional or appropriations. The Governor may not veto a word or sentence within a section,” he said. “What happens next could have a big impact on future legislative deal-making.”

Jerry Cornfield is a political reporter for The Daily Herald of Everett. He can be contacted at 360-352-8623 and jcornfield@heraldnet.com.