Lees-Galloway has previously said that the decision was one of the hardest he has had to make.
National's immigration spokesman Michael Woodhouse, a former immigration minister, said it was an "extraordinary development" about an arrogant and reckless minister.
"A case that the Prime Minister described as needing careful consideration and deeply complex was decided possibly within minutes, probably at most within an hour.
"This was a terrible decision made by an arrogant minister who didn't look at his papers properly ... It's reckless, frankly."
He said the minister might not read the whole file and rely only on the summary if the decision was about upholding deportation liability.
"When consideration is given to suspending or cancelling deportation liability, a deeper analysis is required. On a complex case like this, it would be absolutely vital. That's what the minister said he had done, but we now know that to be patently false."
He said Lees-Galloway was unfit to be a minister.
"He is solely responsible for this debacle. No one else."
Lees-Galloway said he has looked at the whole file since the original decision.
"I'm still confident that, given the information I had available to me at the time, I was able to make a decision ... I was thorough in making that decision."
A further allegation emerged today that Sroubek may have threatened his estranged wife.
In Parliament today, National's deputy leader Paula Bennett asked the Prime Minister whether Police or Immigration New Zealand had a phone record of threats made by Sroubek from prison to his estranged wife on May 3 this year.
"Are they considering that as part of their investigation?" she asked.
Minister Chris Hipkins, responding on behalf of the Prime Minister, said the investigation would look at all the information Lees-Galloway was presented with when he made his decision, and whether that was complete.
Under questioning from National, Lees-Galloway confirmed he met his officials at 4.30pm on October 19 and made his decision that day.
Earlier today, Sroubek released a statement through his lawyer, saying that "much of what has been said about me and my circumstances does not present the true picture".
He said he had nothing to do with an alleged burglary at a $2.3m Remuera house that took place a few days after he placed a caveat on it.
Yesterday during Question Time, Paula Bennett asked the Prime Minister whether the Immigration NZ investigation would look into the alleged burglary.
"The National deputy leader, by her questions in Parliament, has implied I may have had something to do with an alleged burglary of a property I have an interest in," Sroubek said.
"The allegation I was involved in that burglary is completely without foundation. I was not involved in the burglary."
It was also revealed this week that 2010 court documents showed that a man and his family were placed in a police witness protection programme because of alleged actions by Sroubek and two other men.
Sroubek said he was acquitted in that trial.
"Comments made about that case in the media are not balanced, and in particular do not reflect that the key prosecution witness' evidence was discredited."
Sroubek said he would make no more comment until Immigration NZ finished its investigation into his case.
"Until New Zealand Immigration reports back to the Minister and I have had the opportunity to respond to him on any issue he may wish to raise, I will be making no further comment or statement."
