Gaga, 24, recently performed two shows at the O2 Arena in London as part of her massive Monster Ball tour but some of her security team had to call the police after a woman managed to get backstage and was heading to her dressing room.
The woman had security passes and laminated sheets that had helped her breach security at the venue on December 16.
A source said to UK newspaper Daily Mirror: 'This was a serious breach of security and the woman was heading in the direction of the stage and, more worryingly, Gaga's dressing room.
'This woman had gone to great lengths to produce all the fake documentation so she could move at ease in the holding area backstage.'
Her spokesperson declined to comment on the matter.