A civil rights law firm has put a Louisiana District Attorney's Office on notice of a possible lawsuit over allegations the office excludes black people from juries because of their race.

The MacArthur Justice Foundation on Monday released a copy of a letter it sent to Caddo Parish Acting District Attorney Dale Cox, advising him of the possibility of a lawsuit and demanding his office preserve documents that might be used as evidence in such a suit.

The foundation said it represents African-American citizens of Caddo, a Parish in the northwestern corner of the state, who are concerned prosecutors are motivated by race when they use their authority to exclude potential jury members without giving a reason.

The District Attorney's Office did not immediately return a call for comment.