(CNN) -- Colombia's attorney general removed and disqualified Sen. Piedad Cordoba from the Congress for 18 years for having "promoted and collaborated" with the FARC guerrillas, the attorney general's office said in a statement.
Attorney General Alejandro Ordonez Maldonado made the announcement Monday.
Cordoba is a controversial political figure in Colombia.
She heads Colombians for Peace, a group trying to end to the decades-old war between the government and the Revolutionary Armed Forces of Colombia, known as the FARC.
Cordoba has had a hand in freeing prisoners held by the FARC, including two soldiers released in March, one of them who was a captive of the rebels for 12 years.
Cordoba has had a hand in the release of at least 19 hostages.
The high-profile releases have earned Cordoba praise and a rumors of being a candidate for the Nobel Peace Prize. Critics say that her ties to the FARC are too close for comfort, however.
Ordonez said that the investigation against Cordoba originated from computers seized in a 2008 operation against a top FARC leader, Raul Reyes. Reyes was killed in a Colombian military raid.
The evidence showed communications between the FARC and the senator, who was identified under the aliases "Teodora," "Teodora de Bolivar," "La Negra" and "La Negrita," the statement said.
In these communications with the FARC, a designated terrorist group, Cordoba overreached her functions and authority to negotiate hostage releases, the statement said.
The links found on the computers were corroborated through other channels, including legal phone taps, the attorney general's office said.
On her Twitter account, Cordoba wrote Thursday that she was meeting with her attorneys about the attorney general's decision. "Be calm," she wrote.
Investigators "established with certainty that the senator sent advice to the FARC," the statement said.
In particular, the investigation found that she advised the rebel group not to send videos of hostages and instead voice recordings, with the goal of helping meet the group's agenda, the statement said.
The attorney general's office said that Cordoba instructed the FARC to release proof of life videos from the hostages with the goal of making other countries look favorable. She also made public statements aimed at promoting the rebel group and helping their interests, the statement said.
While Cordoba lost her senatorial post, she was not charged with treason, the attorney general pointed out.