Boston University Professor Nathan Phillips says he entered his office on Friday to find a Pride flag – he’d had hanging from his window – folded up on a chair with a note on top.

The note said the flag was removed “per University police” prohibiting signage on “outward facing windows or doors.” Saddened, Phillips says he put the rainbow flag back up. It was taken down a second time earlier this week – and he put it back up again.

“I just felt very strongly that I really had to maintain the line on freedom of expression,” Phillips told GBH News on Wednesday.

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Phillips is one of several university members who have been told to take down flags or other political signage since last spring. According to a university website, the policycurrently states:

“No unattended placards, banners, or other signs will be permitted, unless they are affixed securely to a location that has been approved for posting (e.g., a Free Expression Board). Any signage used by Event participants may not be affixed to any University-owned property, including walls, windows, or furniture.”

Boston University officials did not respond to a request for comment. But the ongoing dispute has led to increasing concerns from faculty about what they say is stifling free speech. On Monday, a group of faculty representing the BU chapter of the American Association of University Professors sent a letter to BU President Melissa Gilliam.

The letter urges the school administration to, “Support free speech on campus and to stop selectively targeting speech that the Trump administration does not like and rescind the underlying policy.”

Joseph Harris, co-president of the BU chapter and co-author of the letter, said the university policy is infringing on free speech. “This is a clear effort to deliberately try to inculcate some kind of intimidation, to try to silence free speech and call it content-neutral university policy.”

Harris said removing flags and other signage sends a threatening message to the university community. “They symbolize inclusion, welcoming, safety and acceptance,’’ he said. “When those are attacked, communities are attacked.”

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Laura Jiménez, an associate dean of equity, diversity, and inclusion at BU Wheelock College of Education & Human Development, told GBH News she believes the policy is selective. She says flags or signage have been “focused on identities and celebrating identities” including pro-Palestinian flags. In contrast, she said, a Taylor Swift balloon has been left untouched for over five months on Silber Way.

Jiménez, said the Pride flags are special to her because she identifies as lesbian. But, she says, “It’s not selective only to Pride flags. It’s selective to identity fostering, and welcoming signage.”

It appears that the dispute may only be prompting more protest. Several Pride flags were seen hanging in office windows on Wednesday. Jennifer Snyder-Cappione, who works on the BU’s medical campus, said she put up a Pride flag in her her own office after she learned that Phillips’ flag had been removed.

“Where are we going with this and where does it stop? Are we soon not gonna be able to have any type of text on our clothing when we’re at work?” she asked. “This is just a dangerous road to go down and it’s totally unacceptable.”