The local chapter of a group called Veterans for Peace estimated 15 of its members and supporters were arrested Sunday at the event sponsored by the American Legion. Boston Police said several arrests were made, but did not have an exact number.
The detainees were later released on bail.
"We're opposed to the U.S. invasion of Iraq; we're opposed to the planned invasion of Iran," said group member Winston Warfield, a Vietnam War veteran. "A lot of veterans view us as traitors."
Warfield said the American Legion rejected their request to have a speaker at the event, which took place outside City Hall. A call to the American Legion office in Boston was not immediately returned Monday.
"From our point of view, it's a public affair," Warfield said, despite U.S. Supreme Court precedent that allows private groups that obtain proper permits to choose who can participate in their events.
Earlier Sunday, Gov. Deval Patrick and Sen. John Kerry presented medals to five surviving members of the Tuskegee Airmen, the famed group of black fighter pilots from World War II.
"It is an honor to formally recognize these heroic pioneers," said Patrick, the state's first black governor. Legislation was approved last year authorizing a Congressional Gold Medal for the Tuskegee Airmen as a group; it was presented in March. Individual airmen receive bronze replicas.