P!nk Gets Served, Mommy Day Out Interrupted

P!nk's day out with her baby boy was rudely interrupted ... allegedly by Dr. Luke and Kesha's legal war, and it all happened on camera.

P!nk walked out of a building in NYC Wednesday, toting her one-year-old son, Jameson. Paparazzi and fans were waiting for her, and so was a process server. You gotta see the video ... before P!nk and Jameson can make it into their waiting car ... the dude pounces with a piece of paper.

We're told the summons is related to the ongoing lawsuit between Kesha and Dr. Luke. P!nk's been a vocal supporter of Kesha ... calling the case karma for Luke, who she calls "not a good person."