No one else. The 1st Amendment only states the government cannot ban you from speaking, protesting, etc. Private citizens/companies can do that. We have separate laws that protect people from discrimination, which only work in theory, but the 1st Amendment doesn’t. People are not denying Chick-fil-a their 1st Amendment rights by saying we should boycott them and not eat their anymore. Congress cannot pass a law stating no one can eat at Chick-fil-a because of their stance on same-sex marriage. However, the public can tell everyone not to eat their because surprise they have the right to do that. You know, the 1st Amendment applies to them as well. It’s embarrassing how few people understand how the 1st Amendment works.
Emphasis mine because I seriously can’t believe how often I have to explain this to people.