Salut,
C'est vrai. La Rosh Hashana est traditionellement un jour férié au Congress, et ceci depuis très longtemps (tout comme Pessah (pâque juive) et Yom Kippour)
"Representatives get a break for Easter, Passover, Rosh Hashanah, Yom Kippur, and Christmas Day. (...) The holiday schedule can vary from year to year. Leaders from both parties set up a tentative list of days off every January, before Congress convenes. Lawmakers can adjust the schedule as needed and suspend holidays in case of an emergency. (...) In the early days of Congress, when it was more difficult to travel long distances home, sessions lasted only from December to early spring-so the Jewish High Holidays were de facto days off. Members often met on religious holidays that fell within the session, including Christmas Day. (Religious services for members and their staffs were sometimes held inside the Capitol building.) Congress typically recessed for Easter, but on some occasions, such as during World War II, the holiday break was delayed or canceled. It wasn't until 1958 that members began traveling home on the weekends and a yearlong session evolved. Since then, the party leaders have regularly scheduled days off for Christian and Jewish holidays, although there is no official law that requires them."
Source de la citation: http://www.slate.com/id/2201250/