Transportation Secretary, Pete Buttigieg, is here to clear up why the federal government seems to be pushing back on mask mandates that were set to expire.

The cabinet member formerly known as Mayor Pete came on "TMZ Live" and offered some much-needed clarity on the whole mask mandate confusion, particularly on planes -- namely, whether people still have to wear them.

As you know, a federal judge struck down the Biden administration's mask mandate rule for air travel earlier this month -- giving people the right to go maskless if they want -- but since then the DOJ has appealed the decision, and wants to make its case in court.

Of course, the reason people are scratching their heads ... if the federal mask mandate was going to end on May 3 anyway, why are Biden and co. trying to reinstate it?

As PB explains here ... it's not so much that President Biden wants to force people to mask up again, but more so -- trying to define and establish the federal government's legal authority on this sort of issue, which the judge kinda flouted with their ruling.

With that said, Pete says at this moment ... people do NOT have to mask up while flying, as long as the airline doesn't require it -- and none of them do, currently. As for ground-level public transit -- that's up to local, city or county policy.

Check out the full interview on Thursday's "TMZ Live," because we also grilled the Secretary on that infuriating issue affecting all of us ... gas prices!!!

After talking shop ... we kinda nerded out with Pete on his 2 babies, whom he welcomed to the world with his husband, Chasten, last year. We get into the nitty-gritty (and poopy) ... and it sounds like Pete's enjoying parenthood to no end.