A 40-year-old woman accused of stalking Alec Baldwin was arrested outside the actor's NYC apartment last night ... the 3rd time she's allegedly attempted to confront the actor in the past 2 weeks.
Law enforcement tells TMZ ... Genevieve Sabourin, a Canadian actress, appeared at Baldwin's Manhattan pad Sunday night and asked the doorman to buzz the actor.
The doorman called Baldwin -- who was at his OTHER home in the Hamptons at the time -- but the actor instantly recognized her name.
According to the NY Post, Sabourin had allegedly tracked Baldwin down at his home in the Hamptons on March 31 ... and then followed him to an event at the Lincoln Center a few days later ... and frankly, Baldwin was concerned.
We're told Baldwin felt Sabourin had been stalking him to a point where he and his fiancee felt threatened.
We're told Baldwin told his doorman NOT to allow the woman inside his building ... and then he notified police. Cops swooped in ... and arrested Sabourin at the building for aggravated harassment and stalking at 7:45 PM.
Sabourin reportedly met Baldwin while working on "The Adventures of Pluto Nash" back in 2002 ... but recently began bombarding Alec with emails and text messages saying she wanted to have his baby. She also asked to borrow money.
Alec's rep, Matthew Hiltzik, tells TMZ, "As you know, stalking is a serious issue, so we've turned this matter over to the New York Police Department."