Sanhedrin 26 - Seventh-year (Shmita) Merchants
One is allowed to gather produce of the seventh year (Shmita), but not trade in it. Initially both Shmita gatherers and traders were disqualified from serving as witnesses. However, when the ruling power began to collect tax in the seventh year, Rabbi Yannai allowed to plant on Shmita, since Shmita today is only a decree of the Sages. After this only merchants remained disqualified.
Once during Shmita Resh Lakish joined Rabbi Chiya and Rabbi Shimon, to observe the procedure of calculating a leap year. He saw a man plowing and said "This man is a Kohen and he is plowing." (Kohanim were especially suspect). They answered, "He might say that he is just a worker." He then saw a man pruning and said "Kohen is pruning." They answered, "He may say that he needs the branches."
They said, "This fellow is argumentative." When they reached the meeting place, they ascended and pulled the ladder up, to prevent him from joining.
Art: Carl Larsson - Plowing