The Letters of Note blog has an interesting item up on a 1914 letter Bob Fitzsimmons - boxing's first three-division world champion and one of boxings hardest punchers - penned after the boxing commission refused to renew his boxing license. 

Just prior to writing the following letter on his truly magnificent, befittingly boastful letterhead, the boxing commission had refused to renew his boxing license on account of his age (he was 51) and he was clearly furious. Refusing to accept the decision he appealed, but to no avail; his last fight took place that year.