Before us is Mishnah 3 in chapter 6 of Maseches Demai, which deals with a kohen or a Levi who received a field from a Yisrael as a sharecropper.
The view of the first Tanna:
"Kohen v'Levi shekiblu sadeh mi'Yisrael" - a kohen or a Levi who undertook to work as sharecroppers in the field of another Jew, in exchange for a percentage of the produce. "K'shem shecholkin b'chulin kach cholkin b'Terumah" - just as they give the owner his share of the ordinary produce, from the crop whose Terumah and tithes have already been separated, so too they must give him his share even of the Terumah, and this includes both Terumah and the tithe.
The reason for this: the Jewish owner has the right to give the Terumah to any kohen he wishes and the tithe to any Levi he wishes, and not specifically to the kohen or Levi working as sharecroppers in his field. These sharecroppers have no greater claim to it than any other kohen or Levi whom the owner might choose.
The view of Rabbi Eliezer:
Rabbi Eliezer disagrees and says: "Af hama'aser shelahen" - even the Terumah and the tithe belong to the sharecropper himself, the kohen taking the Terumah and the Levi taking the tithe, "she'al menas kein ba" - for this is the condition on which they entered the work.
The kohen came to serve as a sharecropper with the understanding that, since he is a kohen, the Terumah that comes out of this field will be given to him, including the portion that is supposed to reach the owner of the field, since in any case he is fit to receive it; and the same applies to the Levi with regard to the tithe. This is Rabbi Eliezer's view, in contrast to the view of the first Tanna.
In summary: the Tannaim disagree about a kohen or a Levi who received a field from a Yisrael as sharecroppers. According to the first Tanna, just as they divide the ordinary produce, so they divide the Terumah and the tithe, and they must hand the owner his share, since it is in his hands to give them to any kohen or Levi he chooses. According to Rabbi Eliezer, all of the Terumah and the tithe belong to the sharecropper, the kohen or the Levi, because it was on this condition that they entered their work.