Transparency International in Papua New Guinea says it believes the government's move to delay elections is illegitimate.
Papua New Guinea's parliament voted to postpone its national elections for six months, in a surprise vote that passed the House 63 to 11.
Elections will be suspended for six months from April 27, when writs are scheduled to be issued.
In a speech to parliament, Deputy Prime Minister Belden Namah warned against foreign intervention following the decision.
He warned the Australian Foreign Minister Bob Carr, who had threatened sanctions if there was a deferral, not to threaten the independent state of PNG.
Our correspondent Titi Gabi says the government claims issues with the state of the rolls and the poor security in the Highlands.
"The justification is that the common roll is in a mess and there's also security issues, they feel strongly that need to be tightened and reviewed."
Transparency International PNG's Chairman Lawrence Stephens says some lawyers are claiming it can be allowed by the constitution but he says that's not the case.
Anybody who has half an idea of what the meaning of the constitution is all about, it is just illegitimate. The country is galvanised and angry by the decision. It becomes even more hurtful to many people who publicly accepted the assurances from the Prime Minister, on a number of occasions that this would not happen.
Parliament voted to order the Electoral Commissioner Andrew Trawen to ask Governor-General Sir Michael Ogio for the suspension.
AAP reports that Mr Trawen says he is consulting his lawyers over the direction, and has previously said the constitution fixes parliament into a strict five-year term and that the nation is ready to go to the polls.
Australia's Prime Minister, Julia Gillard says there are question marks over whether the decision is constitutional.
She says while her government respects Papua New Guinea's sovereignty, as a strong supporter and long-time friend of the country, Australia believes that the elections should be held on time, in accordance with the constitution.