UPDATED: 4.49PM The sweep through the public service looking for pay irregularities has so far picked up around 24,000 who didn't get what they were entitled to under the Holidays Act.

The Ministry of Business, Innovation and Employment is one of the departments that's experienced pay issues and its Minister Steven Joyce is blaming Labour for bringing the Act in, in 2003.

"There is likely to be more than we know about today because it is quite obvious that some pay roll providers are having some difficulties doing this calculation. On an individual person basis it's not going to have a significant impact on most people's remuneration at all"

MORE: Holiday pay stuff ups means thousands of dollars in payouts 

Mr Joyce said changing it isn't as easy as it sounds.

"There was a lot of people that were very concerned that any impact on people was entitlements. That's the trouble that we get a general consensus that we don't want to change the Holidays Act because we are worried about people's entitlements".

Workplace Relations Minister Michael Woodhouse said they tried to fix the problem in 2010, but couldn't get the changes they wanted, because unions in the working group didn't come to an agreement.

"The methodology is complicated. Employers, pay roll providers will agree that that's the case but the question is how do you simplify it without reducing entitlements".

 Labour's Economic Development spokesperson David Clark said the Government needs to take responsibility, and fix a bad piece of law.

"The Government has known about this problem since 2010 at least. The main problems that seem to result from the Holidays Act go back to changes made in 2011 we've learnt from employment lawyers today"