As Rabbi Herschel Schachter discusses at length (Eretz HaTzvi, 6), rabbinically prohibited actions on Shabbat fall into one of two categories, a) melakhot on a rabbinical level, and b) g'zeirot, which are instituted to prevent biblical melakhot from taking place. The rules for these two categories differ. For example, g’zeirot are automatically suspended for an ill person who is not in danger; a melakhah cannot be violated passively, while a g’zeirah can; and g’zeirot are suspended during bein ha-shemashot (twilight) (Eiruvin, 32b).

Carrying in a carmelit is a g’zeirah; this is evident from, among other things, the fact that the Talmud applies to it the rule that such enactments are inapplicable during bein ha-shemashot (Shabbat 8b). It is for this reason, as R. Akiva Eiger explains (Resp., I, 28), that the rule against a “double g’zeirah” applies to another g’zeirah attaching to carrying in a carmelit (as opposed to two rabbinical melakhot, or a rabbinical melakhah and a g’zeirah, which can in theory co-exist).

However, as R. Schachter observes, following this logic would lead to the conclusion that asking a non-Jew (“amira l’akum”) to carry in a carmelit, even without any other mitigating factor (such as the need of a mitzvah or an ill person, or bein ha-shemashot) would likewise be permitted. He thus explains that while the prohibition of “amira l’akum”is indeed a g’zeirah (to prevent the Jew from coming to perform the act on his own; see Rambam, Hil. Shabbat ch. 6), it also has elements of “rabbinical melakhah” to the extent that it represents some sort of agency on behalf of the Jew. Thus, such a scenario as described above would only be permitted in conjunction with other mitigating factors.