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

ACLU legal director Vic Walczak said Pittsburgh City Councilwoman Darlene Harris is censoring critical comments from her Facebook page and thus violating the First Amendment. The Pittsburgh Tribune-Review reported Walczak wrote a letter Tuesday that asked Harris to unblock four residents she had previously blocked from her Facebook page by Dec. 4.

The letter said if Harris does not respond to the letter or does not unblock the constituents by that date, the ACLU will interpret it as a rejection of the request and will file a lawsuit, Walczak said.

One of the blocked residents, Lora Rigatti, said Harris' Facebook page frequently posts important information for constituents, such as locations of fresh water during August's boil advisory.

Another blocked resident, Chris MacTaggart, said he believes Harris ignores constituents who don't agree with her.

Harris, a Democrat, declined to comment. She previously said Facebook posters were using vulgar language against her.