Who you work is up to you…..but
Stations can work whomever they please. However, it is common courtesy that if you want to restrict your replies to a certain entity, state etc. say so. This morning a station from Central America was operating and working from what I could tell JA’s. He was not showing any signs of restricting his calling (CQ; QRZ) so every so often I called. Keep in mind that when you run 25 watts with an attic antenna (especially under a wet roof) any contact is revered especially one in a not so common entity. At one point he sent DS? only to ignore my call. Only then did he restrict his calling to JA’s only. I have worked many DX stations in the middle of a JA string so I believe calling him when I did was not out of line. As I said, he can work anyone he wishes, but a little courtesy would not hurt.