Up to 3000 mental health nurses nationwide are on strike today after their union and district health boards (DHBs) failed to reach agreements with wage negotiations.

Public Service Association (PSA) members from 15 hospitals are involved in the 24-hour strikes.

The PSA also plans to take legal action against at least one DHB, claiming it has breached the Employment Relations Act.

National Secretary Richard Wagstaff said Waitemata District Health Board and possibly other boards had been repeatedly distributing "highly misleading propaganda" directly to union members.

He wouldn't go into detail about the alleged breach but said the Employment Relations Authority would be called on today to intervene.

DHBs have offered pay rises averaging about 20 per cent, but the workers object to parts of the offer, including cuts in penal rates for some.

Mr Wagstaff this morning said while progress had been made with negotiations between the two parties, there were a few important issues to be ironed out and attempts would be made to do so tomorrow.

"Hopefully we will get a breakthrough on a couple of outstanding issues. There has been a lot of good work done, it's just a shame we got held up over some critical issues."

Mr Wagstaff said if there was another breakdown in negotiations there would be furthers strikes next Monday and overtime bans could also be put in place.

"We are hoping it doesn't come to that, but if we can't get a way through on these critical issues it will."

DHB spokesman Jim Green said significant pay increases had been offered and was disappointed the situation had ended with strikes.

Mr Wagstaff yesterday said many mental health nurses had been sitting on expired agreements for over a year, and many others had been working alongside general nursing colleagues whose pay has increased substantially this year.

He said mental health workers deserved a fair pay deal that reflected the difficult job they did.

Both parties said measures had been put in place to ensure the safety of mental health patients wasn't compromised during the strikes.

The National Union of Public Employees is also claiming a 30 per cent "catch-up" pay increase for maintenance staff at hospitals.

Mental health staff from hospitals in Northland and Hutt Valley are not involved in today's strikes.