I mean this literally, not metaphorically. A report from a leading chess website (h/t Ben Katz and Brad Rothschild):

Iranian grandmaster Ehsan Gahem Maghami informed me of his refusal to play against his fourth round opponent, Israeli Fide Master Ehud Shachar. I told Mr. Gahem Maghami that as an organizer of a international sporting competition I could not accede to his request to change the pairings, so that he could play against another player. The presence of five Israeli players in this tournament was known to all participants since Saturday, October 22. It honors our competition, as does the presence of Iranian players and those from about thirty other nationalities. The motto of our Federation is gens una sumus, we are developing in Corsica an awareness of the positive aspects of the chess sport on our youth. Being complicit to any form of segregation would be unworthy, and in total contradiction with the foundations of our sporting activities. So regretfully I have to exclude the player who unfortunately has stuck to his choice, in spite of my entreaties. I regret it, but I could not shirk our responsibilities.

Apparently, Israel and Iran have been going at it in chess for quite some time:

Apart from the political situation in the Middle East there has been a direct chess rivalry between Iran and Israel during the past two years. It began with a simultaneous chess world record set by GM Morteza Mahjoob in a sport saloon in the "Engelab Sport Complex" in Tehran.

The 29-year-old Iranian GM spent months preparing for his record attempt, which until then stood at 360 simultaneous games, set earlier that year by Bulgarian GM Kiril Georgiev. Mahjoob broke it by taking on 500 opponents and scoring 397 wins, 90 draws, 13 loses (= 88.4%). The effort lasted over 18 hours and was closely followed by the Iranian TV. Big illustrated report with videos.

Last October Israeli GM Alik Gershon broke Mahjoob world record by taking on 523 opponents with a 86% result, and got his name into the Guinness World Records book. This led to international headlines on the lines of "Israel destroys Iran - on the chess board board."