People should spend two minutes to do a little googling and find out that they have been doing this for years for Cinco de Mayo.
If you read the article you’ll see that team management, players and others are saying outright that this is in opposition to the new law.
Politically outspoken Steve Nash (the Suns’ point guard) said today on ESPN that they’re wearing it in “solidarity” with the Latino community because of the latter’s justified concerns about the new law. He didn’t mention Cinco de Mayo.
....although I don’t doubt you’re right about the Suns wearing the jerseys in question on that day in the past.