Pressure is continuing to mount on the Adelaide Zoo to reverse its decision to dump a local ice cream company in favour of another supplier that includes palm oil in its product.

South Australia Senator Nick Xenophon has begun collecting signatures outside the zoo in an effort to force a special meeting.

The move is in response to the decision by Zoos SA to end a contract with local ice cream company Golden North, which spent a year eliminating palm oil from its products as part of a zoo campaign to avoid the ingredient.

It was replaced by Streets, despite its ice creams containing palm oil, which is widely considered a factor in the destruction of rain forests, the habitat of orangutans and other endangered species Zoos SA promotes.

Senator Xenophon had previously introduced bills into the Federal Parliament to require the labelling of palm oil in food products and last year worked with the zoo on its campaign.

"What they've done by dumping Golden North actually goes against their aims in terms of conservation," Sentaor Xenophon said.

"This doesn't make sense. You go to the zoo, there's a big spiel about how palm oil's doing this and that, and then what do we do? Do the opposite of what we're saying. It's hypocritical."

Senator Xenophon hopes to collect the signatures of at least 50 Zoos SA members to bring on a special general meeting of the Royal Zoological Society.

"I just hope that the management and board of the zoo understand that they've done the wrong thing and do everything possible to reverse this decision," he said.