Opponents of a controversial “free speech” rally said Thursday that more than 20,000 demonstrators may turn out on Boston Common on Saturday to denounce racism and anti-Semitism, while law enforcement prepared for possible violence just a week after the deadly protests in Charlottesville, Va.
Earlier this week the Boston Free Speech Coalition was given the green light by the city to hold its rally from noon to 2 p.m. at the Parkman Bandstand, a jewel in the oldest public park in the country. Just over 200 people have said on Facebook that they plan to attend that rally, which is scheduled to feature speakers who associate with the “alt-right,” an offshoot of conservatism that mixes racism, white nationalism, anti-Semitism, and populism.
In response to the free speech rally, Roxbury activist Monica Cannon said she is planning to lead thousands on a 2-mile march from the Reggie Lewis Track and Athletic Center to a section of the Common near Charles and Beacon streets to demand justice for all people and “stand in defiance of white supremacy.”
She said 9,200 supporters have indicted on Facebook they plan to join the “Fight Supremacy! Boston Counter-Protest & Resistance Rally,” but she is expecting “20,000 to 30,000 people.’
Another group is planning a separate “Stand for Solidarity” rally on the steps of the State House. Organizers of that rally said 3,000 people indicated on Facebook they were coming to the event, and another 2,000 expressed an interest in attending.
Both groups said they do not have permits from the city to hold their events, but stressed their constitutional right to gather in protest.
“We have the right to organize and the right to assemble,’’ said Kelsey Taylor, an organizer with the group COMBAT or the Coalition to Organize, to Mobilize Boston Against Trump.
Cannon, who stressed a peaceful gathering, said the march from Roxbury to the Common will begin at 10 a.m. There will “healing spaces” where people can gather to speak along the way to accommodate those who do not want to be on the Common, said Cannon.
In addition, volunteers are being trained by Black Lives Matter representatives from Toronto, Charlottesville, Va., Washington, D.C., and Minneapolis on nonviolent de-escalation techniques, Cannon added.
At the rally at the State House, beginning at 11 a.m., Saturday, 30 marshals in neon vests and arm bands are expected to help keep the peace, one of the organizers said.
With days to go before the rally, police are investigating reports that some radical counterprotesters are planning to bring acid to throw at rally-goers, even at police, a law enforcement official with knowledge of the warnings said. The official is not authorized to discuss the intelligence publicly and spoke on condition of anonymity.
The reports have not been substantiated, the official said, but police are preparing for the possibility of such attacks and being told to seek immediate first aid if they are hit with any substances.
The Boston Police Department has already laid out a series of restrictions, citing public safety concerns. Parking will be prohibited along the march route from Roxbury — on Malcolm X Boulevard, Tremont Street, and Columbus Avenue — and on streets surrounding the Common, police said.
Backpacks and other large bags are subjected to a search. Police are also banning any weapons, objects that could be used to harm, beverage containers, grills, and bicycles, according to a list released by the police.
Meanwhile, police Commissioner William B. Evans, in an open letter to returning college students, urged them “act in a way that would make your school . . . proud” on Saturday.
“Today, I am writing to ask for your help as we prepare for these events,” Evans wrote Thursday. “As I have stated in the past, please act in a way that would make your school, your family, and your city proud and please respect our neighborhoods. Student behavior off campus will be regarded the same as if it were on campus.”
Boston Free Speech Coalition organizers have said that their rally is not linked to organizers of the rally in Charlottesville, Va., that led to bloodshed and one death. Coalition members said they support free speech of any kind — no matter the content — and denounce violence.
But civil rights advocates said the group, which also calls itself the New Free Speech Coalition, is giving a platform to people who spew racial hatred and violence.
The free speech members said they planned this month’s rally in May, after their first event. They event was initially slated for last weekend, but was postponed because of the Charlottesville rally, an organizer said.
Facing a blacklash after the violence in Virginia, some of the speakers began canceling, including Kyle Chapman, who participated in the Charlottesville rally. He later changed his mind.
Chapman gained notoriety earlier this year after a video went viral of him smashing a wooden post over the head of an antifascist protester at a march for President Trump in Berkeley, Calif.
But Chapman wrote on Facebook Thursday that he will be on the Common on Boston to speak: “It’s estimated 10,000 #AltLeft Terrorist will be counter protesting and potentially attacking us,’’ Chapman wrote. “We knew this time was coming. It’s time to honor our ancestors. This event is for the Brave. Cowards stay home.”
An organizer of the free speech rally extended an invitation to the Black Lives Matter movement to speak at the rally.
“It’s up to them if they choose to accept,’’ John Medlar wrote on Facebook. “And they have every right to counterprotest our other speakers. That is, after all, free speech.”
Cannon, whose march is being coorganized by local Black Lives Matter chapters, rejected the offer.
“We don’t need to speak at their rally,’’ she said. “We don’t need their platform. Their platform exudes hate and white supremacy.”Milton Valencia of the Globe staff contributed to this report. Meghan E. Irons can be reached at firstname.lastname@example.org. Follow her on Twitter @meghanirons.