A number of leading tech firms plan to file a brief in favor of transgender rights in a case due to be heard next month in the Supreme Court, Axios has learned.

Apple has been among those leading the charge on the effort, along with the LGBT group Human Rights Campaign. Among the other companies that have signed on are Affirm, Box, Ebay, GitHub, IBM, Microsoft, PayPal, Salesforce, Slack, Tumblr, Yelp, Salesforce, sources said.

Apple had already spoken out on the Trump Administration's move to pull back on Obama-era guidance that interpreted existing law to require schools to let students use the restroom that matches their gender identity. The Supreme Court case, involving Virginia high school student Gavin Grimm, asks the court to weigh in on the same question.

Why it's a big deal: The case is the first time the Supreme Court has heard a case involving transgender rights and comes as both society and legislators weigh how to incorporate the reality that sex and gender are more complicated than once assumed.

Who's not on the list? Facebook and Google are two big ones that have yet to sign on, but names are still being gathered and others may yet join.