BOISE -- The fight over whether Gov. C.L. "Butch" Otter's veto of a bill to repeal Idaho's tax on groceries was valid continued Thursday in the state's highest court.

At the heart of the issue is whether the governor missed his deadline to veto the measure, which passed both the House and Senate with a two-thirds majority. The bill, designed to eliminate Idaho's 6 percent tax on groceries, would have gone into effect in the summer of 2018.

Reps. Ron Nate and Bryan Zollinger filed a lawsuit after the veto, arguing that according to the Idaho Constitution, Otter had ten days from the date the Legislature adjourned to make a decision.

MORE: Otter vetoes bill to repeal grocery sales tax

Otter and Idaho Secretary of State Lawerence Denney disagree, pointing to a 39-year-old Supreme Court ruling that the ten-day clock starts when the bill lands on the governor's desk.

Bryan Smith, an attorney representing the legislators, urged the Supreme Court justices to overrule the 1978 Cenarusa v. Andrus case that set that precedent.

"Confidence in the system is, we apply the plain, clear, unambiguous language of the Constitution - that's what people look to," he said.

Furthermore, the lawyer contended, the Supreme Court should order that ruling applied retroactively, essentially voiding Otter's veto on the tax bill.

Smith noted that Nate, Zollinger and the other lawmakers involved in the suit were taking a political risk by pitting themselves against the governor, and warned that tossing out their case could have a chilling effect on future attempts to correct confusing or unfair rulings.

"If we do not reward pioneers who seek to reform the law with winning in their case, then unfortunately there will be discouragement on the part of legal reformers to bring cases such as this to the court," he said.

RELATED: Idaho lawmakers challenge validity of governor's veto

But attorneys for the governor and secretary of state argued Otter was acting in accordance with a four-decade legal precedent.

"The court will be jerking the rug out from underneath the governor without any notice and essentially punishing him for relying on a longstanding precedent and in the end, that's just bad public policy," attorney David Hensley said.

Hensley also pointed out that resetting the starting line to the date the Legislature adjourns could result in legislators waiting to get bills to the governor in order to run out the clock. Bills automatically become law if the deadline passes without a gubernatorial signature or veto.

"Cenarusa v. Andrus has served really as an appropriate and necessary check against the legislature inadvertantly or purposefully infringing on the governor's veto ability," he said.

Otter has also raised the specter of an $80 million shortfall if the state could no longer collect taxes from grocery sales.

RELATED: Grocery tax repeal bill heads to Idaho governor's desk

Speaking after the hearing, Nate argued those fears were overblown, pointing to projections that Idaho will bring in $242 million more than expected by the end of the next fiscal year.

"The money for this is not a question at all, it's whether relief should go to taxpayers or whether the government wants to spend it up," he said.

The lawmakers said that in the future, they hope to take up important bills earlier in the legislative session in order to get them on the governor's desk before the session ends. The grocery tax bill was passed in the final days of the 2017 session, leaving lawmakers little opportunity to overturn Otter's veto.

The Idaho Supreme Court is expected to take at least several weeks before issuing a decision.