Under certain circumstances you may lose your U.S. citizenship by performing, voluntarily and with the intention to relinquish U.S. citizenship, any of the following acts:
(1) being naturalized in a foreign state;
(2) taking an oath or making a declaration to the foreign state;
(3) serving in the armed forces of the foreign state;
(4) accepting employment with a foreign government;
or (5) formally renouncing U.S. citizenship before a U.S. consular officer overseas.
Now, I don't have any plans to work with the Irish governement or An Garda Síochana (Irish police force) but I think this is a little over the top.
I can, however, see that the US Dept. of Homeland Security wouldn't like a citizen to be working for, say, the likes of the Iranian government but I still think this rule should be amended.