If their establishments are open to the public, generally yes, in my opinion, within reason. And that's okay: if an entity wants to operate a business open to the public, it should be open to all the public (within reason: obviously they can't be compelled to be "open" to customers for which there is no relevant business relationship to be had). So an establishment selling only halal goods couldn't be compelled to sell non-halal goods, but it also ought not be permitted to refuse service to non-muslims.