Black Power is advising its gang members to abide by the anti-patch law in Wanganui but believes some people will still defy police.
The bylaw took effect on Tuesday and prevents anyone from displaying symbols which show membership or support for a gang.
People wearing gang patches in certain parts of the city face arrest or a $2,000 fine. A member of a motorcycle gang was the first to be arrested under bylaw on Tuesday and will appear in court next week.
A spokesperson for Black Power, Eugene Ryder, says gangs are already banned from wearing patches in some restaurants and other private venues, and many will see the bylaw as an extension of these rules and abide by them.
However, Mr Ryder says police may face resistance from some gang members who do not want to give up their patches or personal property to police.
Acting Wanganui area commander Inspector Greg Hudson says police are prepared to enforce the legislation, but will use common sense.
The Council for Civil Liberties says it expects complaints against the bylaw will be made to the Human Rights Commission.
The council says the Wanganui bylaw is an infringement of people's rights to freedom of expression and gives police very invasive search powers.
It believes this may be unlawful and breach the Local Government and Bill of Rights acts.
The Human Rights Commission says it has not received any complaints yet, but believes the bylaw raises potential civil rights issues.
Timaru considers bylaw
Timaru Mayor Janie Annear says the council is considering a similar bylaw and discussed a ban on gang insignia six weeks ago.
Ms Annear says there is concern more gangs are setting up in the main South Island cities of Christchurch and Dunedin.
Timaru police and the Chamber of Commerce support the idea of a bylaw, the mayor says.