The public should be able find out what MPs are spending taxpayer money on, the Law Commission says.
A major review of the Official Information Act (OIA) by the commission, released yesterday, said the legislation should be extended to all publicly-funded agencies including courts and Parliament.
This would mean official information requests could be made to the Auditor-General, Office of the Clerk and Parliamentary Services.
Lead commissioner for the report Professor John Burrows said: "We think there's a case now to for saying if a body is receiving public funding and is performing a public function it should be accountable under the OIA."
At present, ministers are subject to the Act but MPs' expense claims cannot be obtained by OIA requests.
The previous Speaker, Margaret Wilson, argued for opening MPs' expense claims up to the public, saying it would help to improve trust if expenses were scrutinised.
The commission has made more than 100 recommendations in "The Public's Right to Know", which aimed to upgrade the Act for the digital age.
Prof Burrows said several major changes in the last three decades had prompted the need for a modernisation of official information laws.
The internet era had made it possible to release vast amounts of information, the public were increasingly demanding more information from central and local government, and the state was more involved in commercial operations.
The commission recommended that agencies pro-actively released data, a policy which would save the public from the need to ask for information, reduce the hassle of responding to individual requests, and ensure more people had access to it.
"In the modern age this is surely the way to go and should be encouraged," Professor Burrows said.
The commission recommended the establishment of an oversight body - similar to a Privacy Commissioner or Human Rights Commissioner - who could act as a champion for the Act.
At present, the Ombudsman was in charge or investigating complaints under the Act, but they did not have any wider responsibilities.
Prof Burrows also said agencies' reasons for refusing information needed to be tightened. The most unclear grounds for refusing to release documents were commercial sensitivity, privacy and the compromising of free and frank exchange.
The commission would also adjust the grounds for refusing requests which imposed too great a workload on agencies.
Prof Burrows said the commission had been told of OIA requests which had taken 300 hours, or seven weeks, to process.
The Justice Ministry and Department of Internal Affairs would consider the recommendations, and were expected to act on them within six months.