Queensland Premier Annastacia Palaszczuk has denied her cabinet is ever asked to vote and says a union leader instructing a minister on where to place his support was "stakeholder consultation".
The Liberal National Party wants the corruption watchdog to probe the 2015 incident for a possible breach of cabinet confidentiality.
The email conversation involving former Electrical Trades Union secretary Peter Simpson and then energy minister Mark Bailey was first revealed in a report made public on Wednesday night.
Mr Simpson emailed Mr Bailey telling him he would get "three options to vote upon" at a cabinet meeting about workers compensation the next day.
"We obviously hope you go for A," the ETU secretary wrote at the time.
Mr Bailey replied: "Will give you a call in the morning comrade, M."
When asked on Friday if it was normal for union leaders to instruct ministers how to vote in cabinet, Ms Palaszczuk was incredulous.
She insisted that could not have happened because there were no votes in her cabinet meetings.
"No one votes at cabinet," Ms Palaszczuk told reporters.
"It's not like a parliament where you come in and take votes, cabinet does not operate that way."
The premier said the emails between Mr Simpson and Mr Bailey were "stakeholder consultation".
It was normal practice, she said, for ministers to speak with various interest groups about upcoming policy and law changes.
Ms Palaszczuk denied it was "disturbing" that Mr Simpson knew what was on the cabinet agenda ahead of time.
"That is a hallmark of good government, to have stakeholder consultation," she said.
Former state archivist Mike Summerell's 2017 report, which contained the controversial emails, was published for the first time on Wednesday night.
He wrote that the emails could indicate a breach of the ministerial code.
"The seeming ETU awareness of what Cabinet was discussing or about to discuss, sometimes in detail, was alarming," the report said.
LNP leader David Crisafulli said the premier should refer the matter to the Crime and Corruption Commission if she "values integrity".
"This is an issue of cabinet documents being shopped around like they're some sort of trivial bit of information. These are cabinet documents, going to union bosses," the Opposition leader said.
He said union officials could still be instructing government ministers how to vote in cabinet, which was unfair to voters.
"Because Queenslanders don't get to vote for union officials, they get to vote for politicians," Mr Crisafulli said.
"Now this is a complete breach in the way the democratic process should work and anything short of an inquiry from the CCC won't cut it."
The corruption watchdog was made aware of the emails between Mr Bailey and Mr Simpson, who died in 2020, five years ago.
The CCC said in their 2017 investigation that Mr Bailey had not broken any law by using his private email for official purposes, but it was in breach of ministerial standards.
It also said while using private emails for official business was a corruption risk, there was no evidence of wrongdoing in this case.
"The CCC did not identify any evidence to support allegations Minister Bailey had used his personal email account to engage in negotiations with the Electrical Trades Union that would amount to corrupt conduct," the watchdog's report said.
