Workers whose employment or self-employment would otherwise be covered by both the
U.S. and Polish social security systems are covered and taxed for social security
purposes by only one country's system beginning March 1, 2009. The agreement does
not affect a worker's taxation or coverage prior to that date. If a worker had earnings
before March 1, 2009 that were dually covered, those earnings were subject to social
security taxes in both countries.