Apple, IBM, Microsoft, PayPal and Yelp and others have agreed to sign on to the brief. Other companies may join them prior to the filing.
This is unlikely to be entirely about political correctness. These technology companies require the broadest possible pool of talent. If these efforts help them attract qualified people then their interests will be well served.
These companies have also been instrumental in fighting North Carolina's HB2 as well as Trump's travel ban. In years past, many were on the forefront of the fight for marriage equality.