The Cook Islands opposition says a purse seine fishing agreement with the European Union is invalid because it's been signed off incorrectly.
However a government spokesperson, Edwin Pittman, says the government is yet to complete the Sustainable Fisheries Partnership Agreement.
But the opposition leader, Teina Bishop, insists it has been approved by cabinet and merely needs to be rubber stamped by prime minister Henry Puna.
He says the document was initialled by the Marine Resources secretary for the EU to endorse, but under the 2005 Marine Resources Act, only the minister, who happens to be Henry Puna, can do that.
Mr Bishop says he just made the discovery this week and will be writing to the EU's ambassador and other regional agencies to state his concerns.
"It is invalid, it's illegal, it is invalid because you're giving access for foreign states to come and access your marine resources. I think it will be an embarrassment to cabinet and to the government."
Teina Bishop says the Cook Islands should back out of it by throwing it out of parliament.
The US$6.5 million deal would grant access to four EU purse seiners to catch up to 7,000 tonnes of tuna a year in the Cook Islands' expansive Exclusive Economic Zone.
However, the deal has been controversial, with large protests staged against the proposed deal last year.