Providence Firefighter Stephany Blackwell and others gather Thursday at the union hall to assemble picket signs.

The Providence Journal / Frieda Squires

PROVIDENCE — As if the protests and cancellations weren’t enough, this weekend’s U.S. Conference of Mayors gathering drew more unwanted attention Thursday when the Rhode Island Affiliate of the American Civil Liberties Union called on Mayor David N. Cicilline to stop using an online registration form for people who plan to protest or picket at the event.

In a letter hand-delivered to the mayor’s office, the affiliate’s executive director, Steven Brown, said the form posted on the city’s Web site could have a “chilling effect” on people who want to exercise “their First Amendment rights” at the event, because the form says nothing about the registration being purely voluntary.

“If you went to the Web site and just read the documents that were there, a person would have no inkling that they did not have to register in order to protest this weekend,” Brown said in an interview.

The ACLU also objected to one of the public viewing guidelines listed on the city Web site, which states “bags and backpacks” would be subject to searches, and it questioned the city’s plan to designate areas where people can stage demonstrations.

Brown said the ACLU was not planning legal action as of Thursday afternoon but would take a wait-and-see approach. If nothing happens to people who protest without registering, if the police refrain from searching bags and backpacks without cause and if protesters are allowed to gather within a reasonable distance of the events, then legal action is not likely, he said.

While the online registration form also prompted objections from at least three City Council members, Cicilline said in a statement Thursday that it is “consistent with what other cities have done when holding large conferences such as the U.S. Conference of Mayors” and will help the city to manage resources and ensure safety.

As of mid-afternoon Thursday, two groups had registered to picket or protest: the United Food and Commercial Workers Union, and a political blog known as RiFuture.org, according to the city’s Traffic Engineering Division.

The conference, which runs Friday through Monday, is expected to draw nearly 200 mayors from across the country. It also had been expected to play host to Vice President Joe Biden and other high-ranking officials in President Obama’s administration, until they pulled out late last week in response to demonstrations planned by city firefighters and police officers, who are at odds with Cicilline over contract issues.

While the city and ACLU seemed to be in agreement that establishing areas for protesters is legal as long as it keeps them within “sight and sound” of the place or event they are targeting, it was not clear what the policies will be for dealing with people who stray from designated areas and handling searches of backpacks and bags.

Police Chief Dean Esserman said he needed to review the ACLU’s concerns before talking about searches. When asked how the police will deal with protesters or picketers who wander out of designated areas, he said only that he “is optimistic that we’ll all work well together out there and people will be cooperative.”

Brown and Peter Gaynor, director of the city Emergency Management Agency, said the concept of keeping protesters within sight and sound of the targeted event comes from federal case law.

“Any restrictions for security and crowd control can’t undermine the whole purpose for protesting in the first place,” Brown said. “If you move people to where the protesting is essentially a futile exercise, the city has gone too far.”

Gaynor said the designated locations — such as the Providence Journal side of Sabin Street or the Rhode Island Convention Center — are intended to be places where people would normally protest, without risking getting hit by traffic.

The concerns about Cicilline’s security plan have prompted the City Council to consider an ordinance that would preserve the right to protest but clarify when advance notification is needed.

redgar@projo.com