The U.S. government wiretapped President Trump's former campaign chairman Paul Manafort as a part of an investigation into work done by Washington consulting firms for Ukrainian politicians.

CNN reported Monday multiple intelligence community officials confirmed Manafort was under surveillance due to a secret Foreign Intelligence Surveillance Act, or FISA, court order for an FBI investigation into the consulting work. The wiretap ended at some point during 2016 due to a lack of evidence against Manafort.

However, the FISA court issued a renewed order for surveillance on Manafort that began again late in 2016 and continued at least through the beginning of this year.

During that time frame, Manafort was in communication with President Trump. It's unknown if any of Manafort's conversations with Trump were picked up during the surveillance.

Manafort's political and business dealings with Russian and Ukrainian officials are under scrutiny in the various investigations into Russian meddling in the 2016 election.

Manafort has been singled out as one of the key players, to the point that the FBI carried out an early morning raid on his home earlier this summer.

Manafort worked for Trump between May and August 2016 as campaign chairman and his dealings with Ukraine eventually led to his ouster. According to CNN, the court ordered surveillance against Manafort began again after his departure from campaign because FBI investigators noticed contacts between Trump associates and the Russian government.

Trump has alleged in the past President Obama ordered intelligence officials to wiretap Trump Tower. The Justice Department shot down those claims earlier this summer and said no such evidence exists.

Jamil N. Jaffer, founder of the National Security Institute at George Mason University's Scalia Law School, said the report means trouble for Manafort. Jaffer worked in the Justice Department's National Security Division during the Bush Administration and has experience with the FISA court.

"The fact that DOJ lawyers were able to obtain multiple FISA court orders on Mr. Manafort, including a physical search order, is quite troubling," Jaffer said.

"Indeed, given the stringent requirements that must be met, both at senior levels in the executive branch, as well as with the FISA court judges, to conduct such surveillance of an American in the United States, much less a senior campaign official in the course of an ongoing Presidential campaign, such an effort suggests significant cause for concern,"

The screws appear to be tightening on Manafort.

On Sunday, California Sen. Dianne Feinstein, a Democrat, said it's "likely" the Senate Judiciary Committee will issue a subpoena for Manafort.

And to make matters worse for the former Trump campaign charman, the New York Times reported Monday special counsel Robert Mueller plans to indict Manafort.

Manafort is under investigation for violations of tax law, money laundering, and failing to disclose his lobbying activities, according to the report.