Bella Hadid's readying for legal battle with Adidas ... with sources telling us she's hired legal counsel to take on the athleticwear giant.

Sources familiar with the situation tell TMZ ... Bella's retained lawyers to take action against Adidas for their lack of public accountability -- basically, saying she feels they spearheaded a cruel and damaging campaign.

Our sources say she's upset the company would put out a campaign that would associate anyone with a tragedy like the Munich Massacre at the 1972 Olympics ... with violence running in contrast to BH's own views.

BTW ... we're told Bella's still under contract with Adidas despite earlier reports saying the company dropped her.

ICYMI ... Adidas made Bella the face of a retro sneaker referencing the 1972 Munich Olympics where 11 Israeli Athletes were taken hostage and murdered by terrorists.

Adidas apologized, saying they never meant to make a statement via connection to historical tragedies. Earlier today, Adidas announced it was revising its campaign.

Sounds like Bella's telling people in her orbit she didn't know what she was getting herself into when she signed on ... and, she's holding Adidas responsible for that.

We've reached out to Adidas ... so far, no word back.