Promised changes to New Zealand's welfare system could be years off, the Minister for Social Development says.

A major reform has been promised but it's costly, and Carmel Sepuloni told Newshub Nation she wants expert advice before making decisions.

"To expect me to put the brake on mid-air and turn that jumbo jet around immediately is a little bit unreasonable," she said.

Ms Sepuloni said she would be calling in an expert panel to help her make a decision.

Labour campaigned on ditching the penalty for mothers who won't tell the Ministry who the father of their child is - but now it seems they're in no rush.

"I'm absolutely committed to ditching that sanction, but it would be done within the next three years," Ms Sepuloni said.

It's a response which has disappointed campaigners against poverty.

"Every day, every week, 17,000 children are being affected by that. The Government could act really fast," Sue Bradford of Auckland Action Against Poverty told Newshub.

However ditching the sanction won't come cheap. Ms Sepuloni said it would cost $380 million in total - $95 million a year, for four years.

The expert panel will decide the changes but advocates say time is of the essence, as more than 270,000 Kiwis are on the benefit.

Newshub.