In my country, many public service jobs have limitations on what you are allowed to do extra. Anything that could damage the trust in the public institution in question is off limits. I work in a public office ( government agency) and have to tell if asked what other engagements I have.
Considering what the price is already when I fly from/to Sweden, or really doesn't matter to me if I have to pay an extra 1000円 . Also, those money are earmarked for airports/tourism anyway, don't mind it.