An immigration lawyer is backing National's criticism of the Government over the border re-opening

National says the Government's failed to scale up Immigration New Zealand - and it's keeping families apart for longer.

From April 13 Australians can enter New Zealand and from May 2 people from visa waiver countries can -- but those from other countries have to wait longer.

Immigration Lawyer Aaron Martin says the department has had issues managing workflow for years.

He says Minister Kris Faafoi seems to have been reluctant to get involved to iron out issues.