Associate Immigration Minister Kris Faafoi had refused to intervene in four of the five most recent cases.
"Now we have this Czech, who entered New Zealand using a friend's passport, who is a gang associate and is currently in prison for importing $375,000 worth of drugs," he said.
"Making him a citizen means he can never be deported."
Sroubek arrived in New Zealand in 2003, claiming that he was fleeing from corrupt police after witnessing a murder. Under the name Jan Antolik, he built a new life as a businessman, a representative-level kickboxer and a Hell's Angels associate.
He subsequently admitted criminal ties in the Czech Republic, but has been acquitted, or had convictions overturned, on several charges relating to drugs and robbery in New Zealand. He is now serving a prison term of five years and nine months for using his drink importation business as a front to smuggle 5kg of MDMA, also known as ecstasy, into the country.
He was refused parole last month, Parole Board panel convenor Judge Phil Gittos describing him as evasive, long-winded and "in many respects manifestly untruthful."
Sroubek was to have been deported after completing his sentence, but last week Mr Lees-Galloway confirmed he had granted him residence, subject to "significant conditions," which he declined to reveal.
National's immigration spokesman Michael Woodhouse the information he had did not come close to any threshold where special consideration should have been given by the minister.