PROVIDENCE, R.I. (AP) — Brown University is delaying a return to in-person instruction until October and the University of Pennsylvania said Tuesday it won't open dorms to the vast majority of undergraduate students this fall, joining their Ivy League colleagues in expanding a push toward online instruction amid the pandemic.

Top administrators from Brown, in Providence, Rhode Island, and Penn, in Philadelphia, both cited the high rate of coronavirus spread across the United States and concerns about their school's ability to quarantine large numbers of arriving students to protect public health.

Penn, meanwhile, said severe limitations on testing supplies will make it impossible to carry out its plans for a pretesting regimen.

“The combination of these factors radically constrains our ability to provide a safe and meaningful on-campus experience for our undergraduates,” Penn's president, Amy Gutmann, and other top administrators said in a statement posted online Tuesday.

Penn had already planned to conduct most undergraduate classes online. Penn will allow some international students and others dealing with housing or personal hardships to stay on campus. Its academic calendar remains unchanged, with classes set to begin Sept. 1, it said.

For the fall semester, Penn is reducing tuition by 3.9% and its “general fee” by 10%. Housing and dining fees will be credited or refunded. Administrators said they still hope to allow students back for the spring semester.

Brown's move reverses an earlier plan to begin classes Sept. 9 with many students on campus.

“I want nothing more than to see all of our students back on campus,” the school’s president, Christina Paxson, said in a campus letter. “However, we must make decisions that prioritize the health and safety of the Brown community as well as the greater Providence community."

The school has created a campus coronavirus testing site, trained contact tracers and invested in improved air filtration systems, Paxton said. But if large numbers of students tested positive, the university’s capacity to isolate and quarantine students would be stressed, she said.

Under Brown's updated plan, all undergraduate classes will be taught remotely from Sept. 9 until the week of Oct. 5.

If coronavirus cases fall from their current levels and if the number of students who test positive is low, Brown will invite sophomores, juniors and seniors to campus beginning Oct. 5. If case rates have not improved by Sept. 11, the entire semester will be taught remotely.

For months, Paxson has been a prominent voice calling on colleges to reopen. In a New York Times op-ed in April, she wrote that the “reopening of college and university campuses in the fall should be a national priority.”

But now, Brown joins a growing number of colleges backing away from in-person instruction as coronavirus cases continue to rise.

Princeton had planned to welcome students back to campus, but reversed course on Friday, saying all undergraduate instruction would happen remotely.

“We cannot provide a genuinely meaningful on-campus experience for our undergraduate students this fall in a manner that is respectful of public health concerns and consistent with state regulations and guidance,” Princeton President Christopher Eisgruber wrote in a letter to the campus community.

Most undergraduate classes at Harvard will also be held remotely, with only a limited number of students allowed on campus.

Yale said that most instruction will take place online, though it’s also giving first-year students, juniors and seniors the option to live on campus in the fall, with sophomores, juniors and seniors allowed on campus in the spring.