Prime Minister John Key denies breaking his word with the Council of Trade Unions over labour law changes.
The CTU said its relationship with the government had taken a blow after Mr Key failed to advise it about changes to unions' access to workplace as promised.
In a letter to Mr Key, outraged president Helen Kelly wrote Mr Key had said union access was off the table, and if it changed the CTU would be told.
"You have breached that undertaking," she said.
"You said you wanted to work with the unions. Of course this was at a time of a deepening recession but we thought it was a longer term intention. And you portrayed yourself as a moderating influence in employment law matters. That has changed."
Mr Key said he didn't break his word and he remembered telling the CTU though union access changes weren't a priority, the government was not ruling any future changes to labour laws.
"My recollection ... the primary area of concern was in relation to collective bargaining, something that was in our 2008 manifesto, but I chose not to implement that even though we campaigned on it because it was an issue of significance raised by the unions.
"I vaguely remember them raising the issue about union access, but it was never on the sort of level of a concern that the monopoly was," he said.
"I specifically said 'I understand the Minister for Labour has taken a first look at these issues, this is in relationship to collective bargaining and to union access.
"'The cabinet is yet to consider any recommendation; however, the fact that they are not being progressed more rapidly reflects where they sit in the government's agenda. They are not a driving priority, that is not to say the government is ruling out any future changes to employment law.'"
The government announced earlier this month it intends to extend to all firms the 90-day trial period for new workers; make changes to how the Employment Relations Authority (ERA) operates including less strict processes to sack someone; require permission for union access to work places; allow workers to trade in one of four annual leave weeks for cash and transfer public holidays; and also require workers to provide proof of illness when they take sick days.
Ms Kelly said the changes disregarded "the working people of this country".
"They paint a picture of workers as lazy, untrustworthy skivers that are out of control and need to be disciplined.
"Workers are painted as acting deceitfully when applying for positions, taking sickies, misusing union memberships and a range of other complete generalisations that demean the people we work with every day."
Mr Key said the changes were fair and balanced, and in relation to union access, he doesn't "think it's unreasonable to ask anybody that goes into the workplace just to announce that they are going to go into that workplace."
"I'll leave New Zealanders to judge whether or not it was a moderate and fair programme of employment law. In my opinion it is."
He said the CTU would be able to freely express its concerns to a select committee.
"We try to be constructive with the union movement. We are going to continue to be so."