A National official says Inland Revenue numbers should have been "beefed up" to deal with the high number of calls after almost 700,000 calls were disconnected before they even entered the queue.
The party's revenue spokesperson, Andrew Bayly, said given the changes to the tax system last year, workers should have been increased for the tax season. The period between February and August 2019 saw a 26 per cent rise in calls to the centre, compared with the same period the year before.
"An additional 181,000 callers hung up before speaking with an operator because it was taking too long," Mr Bayly said.
Mr Bayly called on the Government today to fix the issue.
In reply to a written question from Mr Bayly in December, Revenue Minister Stuart Nash said Inland Revenue "now uses broad-based roles which have a wider range of responsibilities".
"This allows Inland Revenue to move its people to focus on the highest priority work, such as answering phone calls.
"Inland Revenue also devoted as many staff as possible to handling customer queries to support customers embed the changes following Release 3 of Inland Revenue’s business transformation."
An Inland Revenue spokesperson told 1 NEWS the agency planned for an increase in caller demand in April last year after tax records moved to the new system, and received 16 per cent more calls than forecast in the first 13 weeks.
"There was high customer interest in the changes resulting in an increase in both the number of calls and the time we spent with each customer. Sometimes customer demand exceeded our ability to answer calls."
Inland Revenue "increased our temporary resources, staff worked overtime, and we moved as many people as possible from across our customer and compliance services group to help answer phones".
More than 300 people were brought in temporarily and 900 staff were used to answer calls.
"This is a balancing act and we aimed to answers as many calls as possible while maintaining other priority work. We believe this is a responsible use of resources.
"Of course, we’d like more calls to be answered but it’s important to remember that Inland Revenue is part way through transforming the tax system and customers naturally have questions about how the changes affect them."
The spokesperson said they encouraged people to use other channels such as going online for simple tasks.