It's basically what stopped a good reform from being introduced by the League of Nations:
"Thus, once or twice a year there would be eight days rather than seven between consecutive Saturdays. Thus the Jewish Sabbath, which must occur every seventh day, would be on a different weekday each year. The same applies to the Christian Sabbath. [British Chief Rabbi] Hertz realised that this would cause problems for Jews and Christians alike in observing their Sabbaths, and mobilised worldwide religious opposition to defeat the proposal."
"Thus, once or twice a year there would be eight days rather than seven between consecutive Saturdays. Thus the Jewish Sabbath, which must occur every seventh day, would be on a different weekday each year. The same applies to the Christian Sabbath. [British Chief Rabbi] Hertz realised that this would cause problems for Jews and Christians alike in observing their Sabbaths, and mobilised worldwide religious opposition to defeat the proposal."
http://en.wikipedia.org/wiki/Joseph_Hertz#Calendar_reform