Party leaders have been quick to shift the focus from Nick Smith onto why John Key "failed to act" much sooner in dealing with his minister's mistakes.
Smith quit his Cabinet posts this afternoon over two conflicts of interest in letters he wrote regarding a friend's ACC claim.
Labour Party leader David Shearer said Smith had done "the honourable thing" in resigning but the Prime Minister had enough information and cause to sack Smith yesterday.
"John Key had that information yesterday morning and he failed to act," Shearer said.
Smith's actions were a clear and "significant" breach of Cabinet guidelines and it was "completely wrong" of him to advocate for a friend in his ministerial role, he said.
New Zealand First leader Winston Peters also hit out at Key, who he said had been aware of Smith's letter for months.
"The Prime Minister should have sacked him a long time ago," Peters said.
"The Prime Minister was aware of this issue a long way back. That's a fact and he can't bluff it out any longer."
Peters said Key had been "tawdry" in applying his own high standards.
In his statement to the House today, Smith attributed his resignation to two letters he wrote, one in July last year and the other in 2010.
But Shearer said bringing up the second letter was a "smokescreen" for John Key.
"I think he's using the second letter as a smokescreen for the fact that he didn't act earlier."
Green Party ACC spokesperson Kevin Hague agreed with Shearer, saying Key should have dealt with it sooner.
"The second conflict, which Dr Smith said led to his resignation, has provided a convenient excuse to get him out of the way when John Key finally cottoned on to how politically damaging the situation was."
Hague said Key "should have had the guts to sack or stand Nick Smith down two days ago" when it became obvious Smith had used his ministerial influence to help a friend in her dispute with ACC.
Peters, Shearer and Hague made a unanimous call for a full scale inquiry into the matter.
Hague said Key must order an independent inquiry into Smith's behaviour.
"There must now be a thorough investigation into this matter so that New Zealanders can be reassured that there has been no further wrongdoing on the part of Nick Smith, John Key or other MPs who may be caught up in this case."
Hague also criticised the way Key has deflected calls for an investigation on to the Privacy Commissioner's inquiry.
There is no scope within the Privacy Act for the Commissioner to inquire into the behaviour of MPs, Hague said.
"That the Privacy Commissioner should investigate a potential misuse of ministerial power was always ridiculous."
Labour deputy leader Grant Robertson said after Smith's resignation that it was clear Smith was a "close associate" of Pullar and that ministerial standards had reached a "new low".