The Centre for Bio-Ethical Reform, based in California, already displays pictures of first-term aborted foetuses on billboards on the sides of trucks, as well as pictures of what it claims are aborted limbs on its website home page. Now it wants to take its message to the skies.

Robert Muise, a lawyer for the centre, told three judges from the San Francisco-based ninth US circuit court of appeals that flying the pictures over sunbathing holidaymakers was the only way his clients could make their point effectively. "That's the essence of their message," said Mr Muise. "Those pictures convey messages that are rhetorically inexpressible."

Claiming the ban violated freedom of speech, the organisation said it also effectively thwarted their ability to engage in public debate and influence opinion. They are seeking protection under the first amendment, which guarantees freedom of speech.

Jon Van Dyke, the city's special deputy counsel, told the court that the proposed banners would pollute Hawaii's natural beauty and make the island less attractive to tourists. "We have a unique, wonderful place. We have outstanding scenery that people come from all over the world to see. This is important for us who live here, and it's vital to our economy."

The centre has been allowed to fly the banners, some as big as 15.2 metres (50ft) high by 30.4 metres long, from aircraft in 19 states.