The problem is defining "supporter" in legal terms. It's probably easy to exclude the Trump Organization itself, but what about those who do business with them? You could exclude people who directly contributed to Trump's campaign, but does one such person in a company bar use by the entire company? It quickly becomes a bit of a quagmire.

Possible alternative: require preservation of a copyright notice which (among all the usual stuff) condemns Trump and his policies. It gives voice to your protest, without the definitional hassles that enforcing a restriction would have.