Screenshot via Twitter The American Civil Liberties Union (ACLU) issued a warning to Jeff Sessions, shortly after he was confirmed as attorney general on Wednesday night.

"Jeff Sessions confirmed as attorney general. If he violates the Constitution, we'll sue," the organization said in a tweet.

The ACLU is a nonpartisan, nonprofit organization that defends individual rights. The statement follows concerns by lawmakers and civilians who argued that Sessions lacked the judgment to serve as the nation's top cop.

The organization had a similar warning for President Donald Trump after he won the US presidential election in November, promising its "full firepower" should Trump seek to undermine the Constitution or violate Americans' rights with the proposals he campaigned on.

Opponents have pointed to Sessions' record as an Alabama senator and state attorney general — and his vocal support of Trump as indications that he might be a rubber stamp for the Trump administration.

Civil-rights groups and law-enforcement watchdogs contended that Sessions could seek to undo protections for people who engage in lawful protests.

Debate over his nomination culminated in an all-night session on the Senate floor Tuesday, when Sen. Elizabeth Warren of Massachusetts was forced to sit down when she attempted to read a 1986 letter from the widow of Martin Luther King, Jr., who was critical of Sessions.

Warren put Sessions on notice after his confirmation Wednesday night.