The 27-year-old actress and model was one of many arrested in Washington as they demonstrated against Mr Kavanaugh.
His nomination has been embroiled in controversy due to allegations of sexual misconduct against him – which he has stringently denied.
Protesting on Thursday, Ms Ratajkowski held a sign which said: “Respect female existence or expect our resistance.”
Taking to Twitter, she shared a picture of her brandishing the sign, as she wore a white vest and light blue jeans.
She wrote: “Today I was arrested protesting the Supreme Court nomination of Brett Kavanaugh, a man who has been accused by multiple women of sexual assault. Men who hurt women can no longer be placed in positions of power.”
However, many decided to comment on her clothing instead of the content of her sign.
One wrote “put some clothes on and read the constitution sweetheart” while another suggested she would have had more “credibility” had she worn a bra.
However, in the wake of these comments, many have taken to defending her.
“She can wear whatever the hell she wants. Keep fighting Emily,” one said in response to her.
Another said: “Stop telling women that what they wear is more important than what they protest.”
Others questioned what she should have been expected to wear, as one asked: “She's in jeans and a tank top. What did you want her to wear? A poncho?”
Others queried why her attire mattered at all.
A vote is to be held on Mr Kavanaugh’s Supreme Court place on Saturday.
Based on the public declarations made Mr Kavanaugh is expected to receive at least 51 votes.
Assuming no one changes their stance to oppose him this would see Mr Kavanaugh through to a place on the court.