MADISON, Wis. (AP) — Sen. Steve Nass officially asked the Legislature’s Republican leaders Tuesday to sue the University of Wisconsin System after system officials refused to submit their COVID-19 protocols to his committee for approval.

Nass sent a letter to Assembly Speaker Robin Vos and Senate Majority Leader Devin LeMahieu demanding they file a lawsuit forcing system leaders to submit their policies to the Legislature’s rules committee. Nass, a Republican and longtime UW critic, co-chairs the committee.

It’s unclear what Vos and LeMahieu might do next. Their aides didn’t immediately respond to messages and at least two Republican lawmakers — Assembly Majority Leader Jim Steineke, Vos’ second-in-command, and Sen. Robert Cowles — oppose any legal action.

UW System President Tommy Thompson has called for UW campuses to hold at least 75% of their classes in person this semester. The schools have implemented a range of protocols to meet that goal, including mask and testing mandates.

Nass has been threatening to sue for weeks unless system leaders hand over the policies to the rules committee for approval. Thompson has maintained the system has the legal authority to manage itself and doesn’t need legislators’ approval to adopt policies to protect students and faculty. He has said he would win any lawsuit.

The squabble has caused a rift between Republicans who vehemently oppose any mandates to mitigate COVID-19 and those who still see Thompson, who served four terms as governor, as a GOP icon.