Federal workers sue for the right to call for Trump's impeachment or to #Resist The union is concerned the guidance restricts free speech.

The largest union of federal workers on Tuesday announced it's suing the U.S. government in a bid to get it to drop its latest rules restricting talk of presidential impeachment and whether they should #Resist.

The American Federation of Government Employees, which represents some 700,000 federal workers, said it was concerned that the latest guidance restricted free speech and could be weaponized by politically motivated managers, including those seeking to punish people who express support for the president.

AFGE National President J. David Cox Sr. said, "OSC's vague, overbroad guidance creates an opening for managers and political appointees to go after career civil servants for politically-motivated reasons."

Last fall, the federal government's Office of Special Counsel, or OSC -- which is not related to former special counsel Robert Mueller -- warned federal workers that lobbying on behalf of any political candidate while on duty or in the office would be a violation of a decades-old law, known as the Hatch Act. The OSC also warned that workers shouldn't advocate for or against Trump's impeachment, insisting that too would be a violation of the Hatch Act.

The law is intended to prevent federal workers from using their position in government to try to sway elections.

American Oversight, which is representing the union in the lawsuit, said the union doesn't oppose the Hatch Act, but warns that specific restrictions on how workers talk about impeachment and possible "resistance" goes too far. The group's executive director, Austin Evers, said the goal of the lawsuit is to protect the right of workers to "blow the whistle on bad policy and criminal activity."

"The Office of Special Counsel has improperly conflated the duties of public service with partisan activity, and by doing so trampled on the First Amendment rights of federal employees and created a chilling effect on dissent within the government," he said.

OSC declined to comment, citing pending litigation. In its November memo, the office defended its decision.

"Assuming that disqualification from holding federal office would bar an individual from serving as president, any advocacy for or against an effort to impeach a candidate is squarely within the definition of political activity for purposes of the Hatch Act," OSC wrote.

Trump's supporters have alleged that the president's agenda is being undermined by federal workers who are part of a "Deep State." Trump has tweeted about such a conspiracy, specifically alleging that the FBI could be part of a conspiracy working against him.

Several senior White House and administration officials have received warnings from the OSC of violations, including White House counselor Kellyanne Conway, former U.S. Ambassador to the United Nations Nikki Haley and White House social media director Dan Scavino Jr. The Hatch Act does not apply to the president or vice president.

In its memo to the nation's estimated two million workers, OSC said overt politicking at the office and online -- including the hashtag #Resist -- violates existing laws intended to keep the day-to-day operations of the government apolitical.

The OSC memo said context matters, however.

For example, criticizing a White House policy while chatting with coworkers might be acceptable, OSC said. But doing it in the context of the 2020 election? That could pose problems, according to the memo.

"There are no 'magic words' of express advocacy necessary in order for statements to be considered political activity under the Hatch Act," according to the memo. "Therefore, when a federal employee is prohibited by the Hatch Act from engaging in political activity -- e.g., when on duty, in the federal workplace, or invoking official authority -- the employee must be careful to avoid making statements directed toward the success or failure of, among others, a candidate for partisan political office."

An OSC spokesman declined to comment, citing pending litigation.

Editor's note: This story has been updated to clarify that the lawsuit specifically objects to the OSC ruling as it pertains to impeachment and "resistance," and does not object to Hatch Act restrictions on advocating for a political candidate.