Gwyneth Paltrow -- Gate Rights Advocate

Gwyneth Paltrow looks down at her neighbors ... from a gate that's illegally high ... so says a pissed-off homeowner who's filed a complaint over her above-it-all entrance.

TMZ has learned ... one of Gwyneth's Brentwood neighbors claims she and hubby Chris Martin built a 9-foot-tall gate in front of their mansion -- WAY ABOVE the legal limit of 6 feet -- and it's an eyesore.

The angry neighbor says no other residents -- including fellow celebs Harrison Ford, Oliver Stone, and Courtney Thorne-Smith -- have gates over 6 feet tall, so why should Gwyneth?

The L.A. City Department of Building and Safety confirmed that it's investigating, and Gwyneth will have 45 days to fix any violations ... or face more than $900 in fines.