The "Mean Girls" star was in her 15th floor room at the hotel, located at 201 Park Avenue South, when she found out Christian LaBella, described as a friend of a friend, had taken several pictures of her while they were hanging out at the nightclub 1 Oak, sources said.
"She wanted him to delete the photos," said police source.
Lohan had been partying with media producer Chanel Omari, actor Theis Jessen and Internet celebrity Cory Kennedy at Catch Restaurant — where Kennedy introduced Lohan to LaBella as her cousin — and the Provocateur nightclub on Ninth Avenue before heading to 1 Oak, sources said.
The party shifted to the hotel room and, by 5:45 a.m., Lohan noticed LaBella snapping photos of her with his cell phone, sources said. In a ruse to delete the photos, Lohan, pretending her own phone was dying, asked LaBella to borrow his phone.
Once Lohan confirmed that LaBella had snapped photos of her throughout the night, she tried to delete the photos, sources said.
"He took offense to that," the source added.
LaBella stormed after Lohan into a bedroom, where the two scuffled on a bed, sources said.
After a brief skirmish, Lohan, 26, darted out of the bedroom and into a hotel stairwell, police said. LaBella gave chase again and caught up to the "Freaky Friday" actress several flights down, sources said.
That's where the two got into it again, sources said. Lohan initially told cops that LaBella grabbed her from behind and choked her, sources said.
A friend of Lohan — a 36-year-old Beverly Hills man who had been in the room, too — came to Lohan's aid and fought off LaBella.
A frantic Lohan called 911 and pulled a fire alarm, effectively shutting down all of the hotel's elevators, police said.
Cops arrived at the W Hotel and covered every staircase entrance and exit. When LaBella finally emerged, cops took him into custody and questioned him at the 13th Precinct stationhouse, police said.
Lohan refused medical attention and was not taken to a hospital, police said.
LaBella — a resident of Valley Village, California, who was reportedly an aide for Illinois Congressman John Shimkus at one time — was initially charged with misdemeanor assault and harassment while detectives investigated Lohan's claim that he choked her, police said. The assault charge was quickly dropped, however, and LaBella was only issued a harassment violation based Lohan's complaint, police said.
He was released from the stationhouse a short time later.
Cops hit Lohan with a harassment violation, too, after LaBella complained that she was the aggressor in the fracas, police said.
The episode marks the latest headline-grabbing incident for the "Herbie: Fully Loaded" star.
Earlier this month, Lohan was arrested outside the Dream Downtown hotel in the Meatpacking District after allegedly striking a restaurant worker with a Porsche and leaving the scene. She was charged with leaving the scene of an accident.
The arrest came just days after Lohan tweeted about the DUI arrest of another actress, Amanda Bynes.
Lohan's legal troubles also include a 2007 driving under the influence conviction, a probation violation and a conviction for stealing jewelry.P
Paul Lomax and Joseph Parziale contributed to this article.