PITTSBURGH — The American Civil Liberties Union of Pennsylvania is threatening to sue a Pittsburgh city councilwoman for blocking constituents on Facebook.

ACLU legal director Vic Walczak says Democratic City Councilwoman Darlene Harris is censoring critical comments from her Facebook page and is thus violating the First Amendment. The Pittsburgh Tribune-Review reports Walczak wrote a letter Tuesday asking Harris to unblock four residents from her Facebook page by Dec. 4.

The letter says if she does not respond or unblock the constituents by then the ACLU will interpret it as a rejection of the request and will file a lawsuit.

Blocked resident Lora Rigatti says Harris’ Facebook page frequently has important information for constituents, such as locations of fresh water during August’s boil advisory.

Harris has declined to comment.