BOISE, Idaho — A lawsuit challenging how long a governor has to veto legislation threatens the constitutional separation of powers, according to an Idaho top official.

Attorneys representing Secretary of State Lawerence Denney responded to the pending legal challenge Tuesday, arguing that the lawsuit blatantly asks one branch of government to not comply with the decision of another branch.

In 1978, the Idaho Supreme Court ruled a governor has 10 days to veto or approve a bill starting when it lands on his desk. However, that decision is now being challenged by 30 lawmakers who argue the Idaho Constitution says the 10-day deadline starts when the Legislature adjourns, not when the governor gets the bill. These lawmakers are now asking the court to overturn its previous decision.

The lawsuit was filed after Gov. C.L. “Butch” Otter vetoed legislation that would have repealed the state’s 6 percent sales tax on groceries. Lawmakers went home for the year on March 29. Otter received the grocery tax repeal bill on March 31. Otter then issued his veto on April 11 — 11 days after adjournment.

The lawsuit originally singled out Denney because he verified the governor’s veto. Otter has since been named in the challenge at the Republican governor’s request because he argued that it was his veto that sparked the lawsuit.

Denney says that he cannot ignore the court’s ruling.

“The principal that neither the Legislature nor the Executive can regulate or alter in any way this court’s jurisdiction is basic to the doctrine of separation of powers,” wrote Deputy Attorney General Brian Kane, Otter’s chief of staff David Hensley and Otter’s legal counsel Cally Younger.

“Once the court has made its interpretation, that holding becomes the rule of law within Idaho. It cannot be arbitrarily ignored or changed by Executive or Legislative Branch officials,” they wrote.

Denney’s attorneys also added that if the court overturned the nearly 40-year-old ruling, it is unknown how many other post-legislative adjournment vetoes would be affected.

“Changing any one veto could create uncertainty within the law particularly if subsequent legislation also impacted a previously vetoed enactment that suddenly became operative,” they wrote.

The Idaho Supreme Court has given state lawmakers seven days to respond to Denney.