The University of Minnesota and Minnesota State public college systems are bringing back mask mandates just weeks before the start of the fall semester to help protect their campuses from the surging delta variant of the virus that causes COVID-19.

The U announced Monday that all students, employees and visitors at its five campuses will be required to wear masks indoors starting Tuesday, regardless of their vaccination status. Last week, Minnesota State Chancellor Devinder Malhotra told presidents of the system's 37 colleges and universities they should reinstate indoor mask mandates if they are located in counties with high virus transmission.

"Wearing a mask or facial covering indoors has been shown to slow the transmission of COVID-19 and, as we saw as a nation, virtually eliminate other airborne illnesses like the flu," U President Joan Gabel said in a statement Monday. She urged those not vaccinated to get their shots.

Neither of the public college systems is requiring students to be vaccinated, despite growing calls to do so.

Minnesota's largest private college, the University of St. Thomas, announced Monday that it will require students and employees to be vaccinated before returning to campus. St. Thomas joined seven other Minnesota private colleges and hundreds of higher education institutions nationwide that have implemented vaccination mandates.

The U's masking requirement applies to all its campuses, even if they are not in a county with high transmission. Minnesota State's mask guidance applies only to colleges and universities in high-transmission areas.

"We expect the number of counties that meet the CDC threshold for 'substantial' or 'high' transmission levels to grow," Malhotra said in a letter to the college presidents. "As a result, all of our colleges and universities should prepare to pivot toward masking protocols, consistent with CDC guidance."

The return of mask mandates at Minnesota colleges suggests the pandemic will continue to impact campus life this fall. Colleges across the country had hoped for a return to in-person classes and activities.

Now colleges are scrambling to determine whether to require masks and vaccines, and some are encountering legal and political pushback on their decisions. Indiana University's vaccine requirement was challenged in court but upheld Monday by a federal appeals court. And Republican lawmakers are trying to block the University of Wisconsin from implementing testing, masking and vaccination protocols.

At the U's Twin Cities campus, nearly 80% of fall classes are slated to be taught in person, according to the university. Faculty members there welcomed the news of a mask mandate Monday.

"I think this mask mandate is a step in the right direction," said Colleen Flaherty Manchester, a professor in the U's Carlson School of Management and vice chair of the school's faculty consultative committee. "There's a big push to get back to campus, which a lot of faculty are excited about."

Dr. Dimitri Drekonja, a U associate professor and infectious disease specialist, said he felt the masking decision was inevitable. What the university should do, he said, is require students and employees to be vaccinated. Several Big Ten colleges, including the University of Michigan and the University of Illinois, have mandated vaccinations.

"I'm still a bit baffled at the university that we seem to be the least rigorous school in the Big Ten about pushing vaccines," Drekonja said. "We don't have mandatory testing, we don't have a vaccine mandate, we don't have any sort of concerted effort to incentivize vaccination for students."

U leaders have argued a vaccination mandate would be difficult to enforce and could be "legally problematic" since the vaccines have been authorized for emergency use but do not yet have full Food and Drug Administration approval.

Additionally, they have noted Minnesota's vaccination law has a "broad exemption clause," including for people who hold beliefs against vaccination.

As for incentives, U spokeswoman Caitlin Hurley said they "haven't necessarily proven to be successful drivers for mass vaccinations," pointing to the shortcomings of the state's program. U administrators were not made available for an interview.

Minnesota State is also being asked to better promote vaccines. About two-thirds of fall classes at Minnesota State's seven universities are slated to be taught in person, while just under half of community and technical college courses will be face to face.

The community college student association LeadMN asked Malhotra on Monday to develop vaccine outreach plans for each system college and university. LeadMN also urged the chancellor to use federal COVID-19 relief funds to pay students to promote vaccination to their peers and to reward vaccinated students with a $250 scholarship.

"This financial incentive can help motivate students that are on the fence about receiving the vaccine as long as it is complemented with a public education effort," LeadMN President Axel Kylander said.

In an interview, Malhotra said colleges and universities are considering putting federal funds toward vaccination efforts and incentives. Institutions will host vaccine clinics and implement safety measures as needed.

Malhotra called on students to get vaccinated as soon as possible, stressing that the fall semester is ultimately "within their control."

"If more and more of our students go and get vaccinated … there is a greater likelihood that these safety protocols and these restrictions will be relaxed sooner than later," Malhotra said.

The Associated Press contributed to this report.