Immigration NZ is investigating claims that contradict the reasons why Immigration Minister Iain Lees-Galloway granted residency to convicted drug smuggler Karel Sroubek.

Lees-Galloway made the announcement this afternoon but is remaining tight-lipped about which claims are being look at, declining to comment on reports that Sroubek's wife no longer supports him and is seeking a restraining order against him.

National Party leader Simon Bridges has also questioned whether Sroubek has returned to the Czech Republic since arriving in New Zealand in 2003, which would challenge any notion that his life might be at risk if he were deported.

Lees-Galloway said the claims were serious, but he was not going to make any decisions based on heresay or innuendo.

If the contradictory information stacks up, it could mean that Sroubek may have committed an offence under the Immigration Act, which could trigger liability for deportation or criminal charges.

Lees-Galloway has also revealed that he granted residency to Sroubek even though it wasn't asked for, saying it the only way to achieve the outcome that he had decided was the right one.

The minister has been under pressure since it emerged that he granted residency to Sroubek, even though Sroubek was found guilty of using a fake passport and is currently in jail for smuggling MDMA.

Sroubek came to New Zealand on a false passport from the Czech Republic in 2003, but was unmasked in 2009 when New Zealand police were given details of his identity and an international arrest warrant on minor charges.

In 2011 he was found guilty of using a false passport, but was discharged without conviction on grounds that he would be in danger from corrupt Czech authorities if he were deported.

He was acquitted of committing an aggravated robbery with two members of the Hells Angels, but in 2016, he was jailed for five years and nine months for importing 5kg of MDMA.

Lees-Galloway has not provided a reason for granting Sroubek residency, citing legal reasons and the need to maintain the integrity of the process.

Simon Bridges has called for Lees-Galloway's resignation, saying his residency decision was "incompetent and naive".

"If he's been wrong here, if ultimately this man is to be deported, [Lees-Galloway] hasn't got the judgement and the skills required in terms of keeping New Zealanders safe with these decisions, and he should resign."

Simon Laurent, a lawyer who has acted for Sroubek, said it would be "quite problematic" if it was proven that Sroubek had returned to the Czech Republic.

"If he had been back to the Czech Republic, and that could be established beyond a doubt – then it would undermine the case for the Minister [to grant residency]."

Sroubek had parole declined last month, and is due back before the Parole Board before the end of September 2019.

In rejecting parole, the board said he was a low risk of reoffending, but noted his links with criminal elements in the Czech Republic, with Hells Angels' members, and called his answers "self-exculpatory, evasive, long-winded and ultimately in our view in many respects manifestly untruthful".

His sentence end date is January 2022