Attorney Roy Bening claimed that killing the men, who maintain they are innocent, would be illegal because they recently filed a second plea for clemency with Indonesia's President Susilo Bambang Yudhoyono. Prosecutors have contested that assertion.
"I am still hopeful SBY will order prosecutors to stop the executions," said Bening, referring to the president by his initials as is common in Indonesia.
Bening said three men received a letter from prosecutors stating they would be shot by firing squad on Sept. 21 in Palu on the island of Sulawesi.
Prosecutors — who do not typically reveal execution dates to the public — were not immediately available for comment.