Shevi'is, Chapter 6, Mishnah 6. In the previous mishnah we learned that we do not take shevi'is produce, or Terumah oil that became tamei, out of Eretz Yisrael to chutz la'aretz, even for the purpose of burning it. In a similar vein, the mishnah here teaches: "Ein mevi'in terumah mi'chutz la'aretz la'aretz" - one may not bring Terumah from outside Eretz Yisrael into Eretz Yisrael.
"Ein mevi'in terumah mi'chutz la'aretz la'aretz":
Outside Eretz Yisrael there are only certain regions in which Terumah is separated, namely the areas close to Eretz Yisrael. But that Terumah, once it has been separated in chutz la'aretz, may not be brought into Eretz Yisrael. The reason given in the Yerushalmi is so that kohanim should not travel out to chutz la'aretz in order to collect Terumah from there.
It is worth pointing out that Terumah in chutz la'aretz is tamei and the kohanim cannot eat it, since the Sages decreed tumah upon all of chutz la'aretz, and consequently the produce grown there is tamei as well. Even so, the kohanim had an interest in it, because they could use it for burning, as was mentioned in the previous mishnah.
The words of Rabbi Shimon:
Rabbi Shimon says something similar to what he said in the previous mishnah: "Shamati b'feirush she'mevi'in mi'Surya, v'ein mevi'in mi'chutz la'aretz":
"She'mevi'in mi'Surya" - just as it is permitted to take produce out from Eretz Yisrael to Syria, so too it is permitted to bring Terumah from Syria into Eretz Yisrael, because for this purpose Syria is considered part of Eretz Yisrael.
"V'ein mevi'in mi'chutz la'aretz" - but Terumah from the rest of chutz la'aretz may not be brought at all.
Here too the Acharonim note a precision in the wording: "V'ein mevi'in mi'chutz la'aretz" - Terumah may not be brought from chutz la'aretz not only into Eretz Yisrael, but even into Syria it is not permitted.