Conservative legal dynamo Ted Olson is joining the fight against North Carolina’s law that requires residents to use the bathroom that correspond to their sex at birth.

The nation’s largest LGBT group, the Human Rights Campaign, has assembled a coalition of more than 200 businesses that oppose the law, which makes life difficult for transgender residents of the state, and on Wednesday announced that Olson would write a friend-of-the-court brief for those companies opposed to the measure.

“HB2 discriminates against fellow citizens because of who they are,” Olson said in a statement. “This law directly challenges the legitimacy of the identity of transgender persons and then compels them to deny it every time they use a public restroom.”

The U.S. Department of Justice is suing North Carolina over the law, which requires residents to use public restrooms that match their gender at birth, not their sexual identity today. The Obama Administration also is threatening to cut off federal dollars from state agencies, including the state’s university system, if North Carolina does not abandon the law.

North Carolina Gov. Pat McCrory has defended the law and is fighting what he calls federal overreach.

Olson, who represented the Bush campaign in the 2000 recount and later served as solicitor general, has become an unlikely ally for LGBT causes. He was co-counsel on the case that overturned California’s Proposition 8 and paved the way for legal same-sex marriage across the country.

“There can be no doubt that this is bad for business in North Carolina,” Olson said. “It demeans business’s customers, it demoralizes their employees, and it contravenes their values of inclusiveness and respect.

Joining Olson on the brief will be partners Ted Boutrous and Matt McGill, who also worked on the California case.

“The safety justifications that have been offered for this law are utterly insupportable,” Boutrous said. “The only danger here is that transgender people in North Carolina will suffer serious and lasting damage because of this law. The business community does not want to be a part of that in North Carolina, or anywhere.”

It’s that business case that the friend-of-the-court brief will look to make. One study has estimated the North Carolina law has cost the economy $500 million and 1,750 jobs. Other studies have estimated the figures are lower, varying from $77 million to $200 million. Companies like PayPal and Deutsche Bank have scrapped plans to expand in the state, and the U.K. has warned its LGBT residents against visiting North Carolina.

Human Rights Campaign President Chad Griffin praised Olson as “one of the nation’s leading conservative legal minds” as he told allies in an email on Wednesday. The group noted that Olson has argued 62 cases at the Supreme Court—and that is likely where this fight over North Carolina bathrooms is heading.

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Write to Philip Elliott at philip.elliott@time.com.