The New Zealand Business Number (NZBN) register will use data from the Inland Revenue Department in an apparent breach Privacy Act that has to be enabled by legislation.
The opposition Labour Party has also questioned whether the new register will make business interaction with government easier and lower transaction costs as intended. Instead it may add a "new and additional" number into the mix rather than replacing other identifiers.
Government agencies have also been lukewarm in their commitment to the programme, Labour said.
"Without a credible timeline in place for whole-of-government adoption of the NZBN, and a tangible accompanying commitment from Government to fund necessary IT infrastructure upgrades, the attempt is unlikely to succeed," Labour said a Commerce Committee report.
The Ministry of Business, Innovatrion and Employment, meanwhile, is already testing the market for IT suppliers to deliver the register.
The report said the NZ Business Number Bill will allow IRD to transfer any primary business data it holds to the NZBN Registrar during a transitional period.
A new clause in the Bill will allow data transferred to "form part of the contents of the register and continue to do so after the transitional period ends, as if consent had been granted".
That process is in breach of Information Privacy Principle 2 of the Privacy Act which requires agencies to collect personal information directly from the individual unless authorised by the individual to collect it elsewhere.
Outlining a series of criticisms, Labour offered only qualified support for the Bill.
"The committee was provided with no convincing reason why the existing IRD number should not be adopted as a universal number for interaction with government," it said in its minority view.
"The Labour Party shares the concern expressed by Federated Farmers that the initial list of government departments does not include agencies such as Worksafe NZ and Immigration NZ. They helpfully suggest swift extension of the number to local government, acknowledging that many businesses have more interaction with local government than central government."
Labour said it shared Chartered Accountants Australia and New Zealand's concern that the benefits for business may be overstated without prompt and broad integration of the NZBN by government agencies.
Only a limited number of government departments have committed to the initial rollout, Labour said.
"The addition of 'yet another number' for businesses and other eligible entities' dealings with public agencies stands in direct opposition to the stated purpose of the bill," Labour said. "Rather than making interactions with government more efficient, a greater cost is incurred in the short term."