They don't want people who could potentially have Covid to fawn over him, creating the risk he could carry the virus back out to the unsuspecting public.
A guard stationed at the gate of the facility said Mittens made three attempts at a break-in yesterday, and despite his undeniable charm, the law is the law.
"Mittens isn't allowed into the facility. We've got to try and get him out if he gets in.
"It was the first time for me seeing Mittens yesterday and he was here three times."
The guard said they had to shoo him away, but he was not too much of a sour-puss about it.
"Mittens is fine with it as far as I'm aware,"
Mittens' dad, Silvio Bruinsma, was not worried about him becoming a vehicle for the virus.
"They have appropriate kind of precautions in place and the security guards obviously do a good job at doing that."
The ball of fluff was under house arrest during alert levels 3 and 4.
Even when he did manage to abscond his isolation, people were very respectful of the Government's rules not to touch other people's pets.
But Mittens missed the attention.
"On the few occasions that he did escape, I have some little children who were his accomplices, shall we say...
"He often came back quite quickly just because he's such a social animal and loves seeing people when if there were people on the street, you know, there weren't people, for him to hang out with."
The fur-midable feline has nearly 60,000 followers on social media, and some of those fans on the streets of Wellington weren't ready to give up the pats, despite the potential Covid risk.
"Mittens is so cute, I can't help it," one said.
Another said he was just out there doing his job, supervising people.
However, it made others pause.
"I have heard cats can carry it, so I don't know. He is around a lot of people. I'm on the fence."
Director general of health Dr Ashley Bloomfield has yet to comment on the repeat offender's attempts to get into the facility.