A proposal to ban camping and other activities at two plazas in San Francisco's Castro District will be considered by the city's Board of Supervisors on Tuesday, and has already prompted the arrest of a homeless advocate in protest of the legislation.

Harvey Milk Plaza and Jane Warner Plaza, both located near the intersection of Market and Castro streets, are the target of the proposal, authored by Supervisor Scott Wiener and supported by many nearby businesses.

The legislation would prohibit the pitching of tents or other structures to camp in the plazas, bar people from sleeping there at any time, and prevent commercial activity there without a permit, among other new regulations.

The plan has drawn the ire of homeless advocates who say it unfairly targets the homeless and is unnecessary because of a state law already barring lodging in public places without permission.

Bob Offer-Westort, an organizer with the San Francisco-based Coalition on Homelessness, decided on Friday night to prove his point by setting up camp in Jane Warner Plaza.

Offer-Westort said that he was arrested only about 30 minutes after arriving at the plaza and was cited at the Police Department's Mission Station for violation of the state law, a misdemeanor that can lead to up to six months in jail and a fine of $1,000.

He said his arrest "proves that camping is already illegal in the plazas."

Wiener said Monday "one can argue that (the state law) applies to camping on the plaza and one can argue it doesn't, but the goal is to make explicit and clear that camping was not prohibited in these plazas."

He said, "It's pretty common to have state penal sections, then to have a local one that's more explicit."

As for Offer-Westort's arrest, Wiener said, "I have a lot of respect for anyone who can pull off a good publicity stunt ... but that doesn't change the fact that we need an explicit piece of legislation to protect our public spaces."

The full board planned to take up the legislation at its meeting scheduled for 2 p.m. Tuesday at City Hall.