CBS News investigative correspondent Sharyl Attkisson announced on Monday that she had resigned from the network after more than two decades, and sources say her departure stems from disagreements over her former employer’s alleged bias.

Attkisson, an Emmy Award-winning journalist who previously worked for CNN, confirmed that she left CBS News with a single five-word message sent from her Twitter account on Monday afternoon.

“I have resigned from CBS,” she wrote.

Moments later, Politico writer Dylan Byers reported on her exit and included remarks made by sources who say they’re familiar with Attkisson’s departure from CBS.

Referring to allegations made by several unnamed sources, Byers wrote that Attkisson “had grown frustrated with what she saw as the network’s liberal bias, an outsize influence by the network’s corporate partners and a lack of dedication to investigative reporting.”

Attkisson has made a name for herself among fellow Washington journalist in recent years as a staunch critic of the Obama administration, and reported exhaustively on the Justice Department’s botched Operation Fast and Furious gun-running scheme and other DC scandals. According to Amazon, she is expected to release a book later this year tentatively titled “Stonewalled: One Reporter's Fight for Truth in Obama's Washington.”

Brains & artistry behind my 2013 Emmy for Outstanding Investigative Journalism:Producer Kim Skeen,Editor Nancy Wyatt. pic.twitter.com/LHYrCyLGp1 — Sharyl Attkisson (@SharylAttkisson) October 12, 2013

Other work attributed to Attkisson in recent months have included reports on the September 2012 storming of the American consulate in Benghazi, Libya and the tainted roll-out of the Affordable Care Act website by the White House, earning her the admiration of several contributors from the conservative-leaning Fox News network, including Stephen Hayes and Sean Hannity.

According to another report published on Monday by Erik Wemple at the Washington Post, Attkisson has become increasingly frustrated in recent months because her reporting on Benghazi and other matters have been routinely nixed from television broadcasts of The CBS Evening News. Wemple went on to site an unnamed source at CBS who said that Attkisson felt she was being kept off the air “because of political considerations.”

In Byers’ article for Politico, he alleged that those frustrations were severe enough that Attkisson approached management with her concerns nearly a year ago.

“Feeling increasingly stymied and marginalized at the network, Attkisson began talking to CBS News President David Rhodes as early as last April about getting out of her contract,” Byers added. “Those negotiations intensified in recent weeks, and her request was finally honored on Monday.”

“It’s been one of life’s great privileges to work at CBS News, and I’m sincerely grateful for the many opportunities I’ve had,” Attkisson said in a statement.