In the days of R. Yehoshua ben Levi they wished to come together and rule than Maaser Rishon may not be given to the Kohanim.

They said, "Who will enter the Beis Midrash? R. Yehoshua ben Levi, who will help the Leviim (since he is a Levi himself)!". He came, but he instead helped the Kohanim. He said, "In 24 places, Kohanim are referred to as Levi. One such place is (Yechezkel 44:15), "...and the Kohanim, the Leviim, the children of Tzadok".

Question: R. Binyamin bar Gidul and R. Acha were sitting and saying, "But the pasuk states (Nechemia 10:39), "And the Kohen, the son of Aharon, shall be with the Leviim at their tithing"? (This indicates that the Kohanim receive Maaser.)

Answer: To give them Terumas Maaser.

Question: But the pasuk states (ibid.), "...and the Leviim shall bring up the tithe (from the tithe)"?

There was a disagreement between Rav Chuna and the Chevraya. One said - the pasuk states (Bamidbar 18:21), "And to the children of Levi (I have given all tithes of Yisrael as an inheritance)". Why didn't it just say 'To the children of Levi'? It teaches that we may give Maaser to the Kohen.

The other opinion said - even without that word 'and', we could still give Maaser to the Kohen. If a person is coming to bequeath his estate to his children and says, "My son Ploni should receive a certain gift and the rest of my estate should be inherited by my children", would Ploni not also be included? (Just because the Kohanim receive the 24 gifts, should that prevent them from receiving Maaser as members of the tribe of Levi?!)

R. Yona gave his Maaser to R. Acha bar Ula, not because he was a Kohen but because he was involved in Torah learning (who should precede a Levi).

What's the source for this? The pasuk states (Divrei HaYamim 2:31:4), "And he commanded the inhabitants of Yerushalayim to give the portion of the Kohanim and the Levites, in order that they be strengthened in the Law of Hash-m."

Rav Huna (who was a Kohen) would not accept Maaser. R. Acha also would not accept Maaser. R. Chiya bar Ba moved to Chutz LaAretz to avoid being pressured to accept Maaser.

A Kohen once asked R. Shmuel bar Nachman if he should accept Maaser. R. Shmuel responded that he should and that which he accepts he should view it as if fell to the tribe of Levi of which he is a member.

R. Yannai ordered his relatives, "When you accept a field as a sharecropper, only accept from non-Kohanim (as if the landowner is a Kohanim he will incorrectly keep the Maaser for himself).

Although one should not give Maaser to a Kohen, if it was already given, one cannot legally extract it from him. Why is this? As the pasuk states (Bamidbar 18:26), "When you take the tithe from the children of Yisrael which I have given you from them as your inheritance, you shall set aside from it a gift for Hash-m, a tithe from the tithe" - you may extract it from Bnei Yisrael but not from a Kohen or a Levi.

Support (R. Elazar): "When you take the tithe from the children of Israel" - you may extract it from Bnei Yisrael but not from a gentile. (If one bought produce from a gentile after the pile was smoothed, he does not need to separate Terumas Maaser from it for the Kohen.)