Sources tell us McGregor and his team landed at Teterbero Airport in New Jersey around midnight on Thursday after flying from Dublin, Ireland.
We're told as soon as the plane touched the ground, it was surrounded by lights and sirens and held on the tarmac while officials boarded the aircraft and checked everyone's documentation.
Law enforcement sources tell us U.S. Customs and Border Protection were the main agency handling the situation.
We're told passengers and crew on the plane were told to turn off their cell phones while their luggage was searched. In the end, at least two members of McGregor's entourage were denied entry into America and sent packing back to Dublin.
It's unclear why the men were refused entry, but we're told McGregor was extremely upset over the situation and ended up heading straight for his hotel and calling it a night.
The Notorious is expected to attend the UFC 229 press conference where Dana White will officially announce the fight between McGregor and Khabib Nurmagomedov.
It will be his first bout since pleading out of his criminal case for the bus incident back in April.
The presser starts at 2PM PT, we'll have to wait and see if McGregor addresses the situation with his friends.