Anti-fluoride activist Pat McNair is livid.
A $600 banner - set up on the corner of Grey and Te Aroha streets in Claudelands - was vandalised last weekend.
Police have been notified.
Anyone with any information regarding the damage should contact Hamilton Central Police on 858 6200.
Between noon and 2pm on Saturday the banner, mounted on the back of a utility vehicle, was attacked and slashed.
Pat says the lobby group calling for an end to city council fluoridation of Hamilton's water supply cannot afford to replace or repair the uninsured banner.
She says Fluoride Free Hamilton was hoping to use the banner till the end of May.
Hamilton City Council is planning a forum to investigate the continued use of fluoride in the city's water supply.