Amicus curiae briefs from interested outside parties—the Latin words mean “friends of the court”—inform appellate judges about what’s at stake in a case. But they also serve another, more subtle purpose, working as a public relations tool for corporations.

On March 3, for example, 53 companies signed onto an amicus brief filed by the Human Rights Campaign in the US Supreme Court case Gloucester County School Board v. Gavin Grimm, supporting a transgender student’s challenge to his school’s gender-conforming bathroom rule as violating federal law.

The 53 corporations together have over 1.3 million employees and generate more than $600 billion in revenue in industries ranging from tech to insurance to cosmetics. In the brief, they argue diversity is good for business and discrimination conflicts with their LGBTQ-friendly corporate policies, harming people and profits. ”These companies are sending a powerful message to transgender children and their families that America’s leading businesses have their backs,” Human Rights Campaign president Chad Griffin explained in a statement.

In other words, the corporations used the brief like a press release, stating positions not only to inform the court but to influence public perception. State and federal courts allow amicus advocacy, but it’s most common in Supreme Court cases.

That is relatively new. In the first century of American high-court cases, amicus briefs were rare, and from 1900-1950 were filed in only about 10% of cases, according to a comprehensive review of amicus advocacy in the Supreme Court published in the University of Pennsylvania Law Review. “This pattern has now completely reversed,” the article notes. Read more via Quarts