MEMPHIS, Tenn. (AP) — Witnesses will be taking the stand during a federal trial in a lawsuit about police surveillance of protesters in Memphis, Tennessee.

The American Civil Liberties Union claims in its suit that the Memphis Police Department violated activists' free speech rights by gathering information on them and monitoring their social media accounts. The city denies the claims, with defense attorneys questioning whether protests and calls to action by activists on social media could have endangered public safety.

U.S. District Judge Jon McCalla is presiding over the non-jury trial. He has already ruled that the city violated a federal consent decree barring the city from engaging in political surveillance. The 1978 order followed disclosures that police spied on civil rights activists.

McCalla will rule on other issues aside from the consent agreement.