SAINT PAUL, Minn. -- The Minnesota Supreme Court on Monday waded into the legal dispute between the Legislature and Gov. Mark Dayton, in a case that touches on at least two major constitutional tenets.

On one hand is the governor's right, under the Minnesota Constitution, to use the line-item veto to knock down any legislative appropriation. On the other hand, is the question of whether the governor has breached the separation of powers clauses in both the state and federal constitutions.

Dayton's attorney, former Supreme Court Justice Sam Hanson, argued that the plain language of the state constitution has no limitations of the governor's line-item veto authority except that it can only be used to undo legislative appropriations.

"If it's an item of appropriation, he's entitled to veto it," Hanson told the justices. "The governor's had that right for 100 years. The governor has the right now. Your decision will not expand that right."

The legislature sued Dayton after he used a line-item veto to wipe out the House and Senate operating budget for the Fiscal 2018-2019 biennium, which began July 1. He did that in hopes of forcing Republican leaders back to the bargaining table, with the goal of convincing them to undo some of the provisions of the tax bill he signed.

He issued those vetoes after the Legislature had already wrapped up a four-day special session and lawmakers had returned home to their districts. So it would take a special session to reopen the tax bill, and to restore those budgets through the legislative process.

The Legislature, however, is asking the courts to strike down Dayton's line-item vetoes and declare the null and void, which would restore the funding.

Doug Kelley, the veteran trial attorney representing the Legislature, asserted that previous high court decisions and other case law on the subject have made it clear the Governor can only use the line-item veto power to strip funding he objects to, not to control the legislative branch.

"We're not here by accident today. We are here because of an engineered situation by the executive branch," Kelley told the court.

"My clients have their hands tied behind their backs."

Kelley and the Legislature prevailed at the lower court level. Ramsey County District Judge John Guthmann ruled that Dayton exceeded his line-item veto authority because he wasn't objecting to the idea of the legislature being funded, but was instead using the power to coerce the legislative branch into changing unrelated legislation.

The timing also made it difficult for lawmakers to respond because only the Governor can call a special session, and he was would only do so under the condition that legislators agree to make changes to the tax bill he already signed.

"As Judge Guthmann said, the legislators are, in essence without a remedy. And that's why we had to come to this court, and that's why you should step in and break this impasse," Kelley explained.

Kelley said it would've been simpler if Dayton had simply vetoed the tax bill, but the legislature had taken steps to make it much more difficult to veto that bill. Republican leaders decided to insert language in to the appropriations bill that would nullify funding for the Dept. of Revenue and its 1,300 employees if Dayton vetoed the tax bill.

The governor referred to that provision as a "poison pill" and a surprise attack by the legislature, while GOP leaders said the governor's staff had at least 39 hours warning about that feature of the appropriations bill. They said they wanted it as an insurance policy to make sure their tax bill would be signed.

The Supreme Court was not considering the constitutionality of the "poison pill" tactic, but Justice Natalie Hudson said it also could be construed as a violation of the separation of powers clause.

"In your brief there's language about the governor using the line-item veto to control, coerce, restrain the actions of the legislature in is exercise of its constitutional powers and duties," Hudson remarked.

"Isn't that exactly what the legislature did by including this poison pill? It was an attempt to control, coerce, constrain the action of the executive branch."

Dayton wanted to make sure legislators and staff members kept getting paid while the case made its way through the court system, so he petitioned the court to order temporary funding until the issue is settled.

That is similar to what happened during government shutdowns in the past, when the courts ordered that "core functions" be funded until the budget impasse could be resolved through the political process.

The legislature also had some carry over funds from 2017, so the legislative branch is funded at least until October 1.

Both parties in the case want a declarative ruling from the state's highest court, rather than to attempt to negotiate an out-of-court settlement.

The court deliberated the case throughout the day on Monday, and may issue an opinion as early as Wednesday morning.