Michelle Williams ain’t going to “Cater 2 U” if you’re taking your shoes off on an airplane … taking to social media to call out her seatmate who went barefoot on a flight.

The singer-songwriter hopped on Instagram to express her displeasure with the person sitting next to her … sharing a snap of their toes — totally uncovered and poking out from behind the seat barrier.

Michelle wrote, “I PROMISE YOU BETTA GETCHO FOOT FROM ME!!!! 🚨 Y’all this is happening neowwwwwwww on my flight and I am crying real tears!!”

MW jokes she accidentally elbowed the foot — so, she’s gotta take her jacket to the cleaners … before lamenting how people in first class feel they can just do whatever they want on planes.

Williams has been busy on Broadway recently … starring in “Death Becomes Her” — the musical based on the 1992 film starring Meryl Streep and Goldie Hawn.

She starred in the original cast in Chicago last year … playing Viola Van Horn — an original character name based on Lisle von Rhuman, who is played by Isabella Rossellini in the OG flick.