Zayn Malik Confronted Yolanda Hadid After She Barged in Gigi's House

Zayn Malik's confrontation with Yolanda Hadid -- the one that ended with Zayn pleading no contest to 4 criminal charges -- was all about boundaries ... boundaries he says she violated.

Sources with direct knowledge tell TMZ ... Zayn was at Gigi's home Sept. 29, where he was staying because he wanted to be close to his daughter. Our sources say on that day Yolanda "barged" into the house, without calling beforehand or even knocking at the door.

We're told this was an ongoing source of conflict ... Zayn felt Yolanda was acting like the house was hers and ignoring his position as the boyfriend of Gigi and father of their little girl. Our sources say Zayn made his feelings known once she entered, but Yolanda wasn't having it.

We're told Zayn typically works nights on his music and sleeps for part of the day, and Yolanda regularly disrupted his life by coming over as if she owned the place.

There were other sources of tension as well ... notably, Yolanda was posting photos of the baby, which pissed off Zayn because he felt privacy was vital.

TMZ broke the story ... Zayn was charged with 4 counts of harassment for allegedly berating Yolanda and pushing her into a dresser -- something he denies. He was also charged with harassing Gigi, who was in Paris at the time of the incident. And, he was charged with harassing the security guard, whom Zayn allegedly challenged to a fight. Zayn pled no contest, received a small fine and was ordered to take anger management courses.