The supermodel debuted her Halloween costume Saturday on the 'Gram, showing that she got all dolled up as Pamela Anderson from her 1996 B-film, 'Barb Wire' ... in which Pammy plays a futuristic badass boss babe/mercenary who takes the law into her own hands.

Kendall captioned the pic with a go-to line of Barb from the movie ... "don't call me babe," while adding her own 2020 spin to it in an effort to encourage folks to hit the polls Tuesday, writing ... "happy halloween! GO VOTE!!!" She also tagged the photog, Amber Asaly.

Instead of Pam/Barb's signature Desert Eagle pistol, Kendall was rockin' "VOTE" flags in its place ... hitting the point home about GOTV. This is right on brand for her, especially of late -- Kendall's really been pushing this and spreading awareness about early voting.

At the beginning of October, she shared a message on IG about early voting starting up in several states, writing ... "did you know that in some states you can early vote???" She added, "you don’t have to wait till November 3rd (that’s also my bday and all i want is for you to vote, pleaseeee and thanks) this is the most important election of our lives! early vote if you can!!! i know i’m going to!"

Great message, no doubt -- and as for the costume ... it's practically flawless. We only say that because as great as Kendall looks, she lacks a certain ... um, Pam-ness, let's call it, that only the '90s-version PA could bring out in all its glory. Solid effort though, we'll give her that.