Sen. Rand Paul, R-Ky., demanded answers to 11 questions about the use of domestic drones in a Thursday letter to FBI Director Robert Mueller, a day ahead of President Barack Obama's nomination of James Comey to replace Mueller.

The last time Department of Justice leaders stonewalled Paul on the use of domestic drones, the likely 2016 presidential candidate stood on the Senate floor for 13 hours to hold up the confirmation vote for John Brennan's nomination to lead the CIA.

"It's too early to tell" if Comey's confirmation vote will be filibustered, Paul's Communications Director Moira Bagley told U.S. News in a Friday email. "We're most concerned with getting these questions answered."

During his March 6 filibuster Paul demanded - and ultimately received - confirmation that the U.S. government cannot use drones to conduct extrajudicial executions of U.S. citizens on American soil. He explained he wasn't specifically targeting Brennan, but rather using the opportunity to highlight an important policy issue.

President Barack Obama speaks during a news conference to announce his nomination of James Comey to become FBI Director in the Rose Garden at the White House, June 21, 2013. (Win McNamee/Getty Images)

In his letter to Mueller, Paul asks how long the FBI has been using drones, how many drones the FBI has, whether or not FBI drones would ever be armed, why they are used, what policies guide their use and what has been done with the information they collect.

"I am disturbed by the revelation that the FBI has unilaterally decided to begin using drone surveillance technology without a governance policy, and thus without the requisite assurances that the constitutional rights of Americans are being protected," Paul said in the letter. "As such, I am requesting your prompt answers."

Mueller's acknowledgement of FBI drone use without clear guidelines Wednesday attracted concern from Senate Judiciary Committee members, including Sen. Dianne Feinstein, D-Calif., who called domestic drones "the greatest threat to the privacy of Americans."

Comey is somewhat of a hero to civil libertarians for objecting to the so-called warrantless wiretapping programs conducted by the National Security Agency during the Bush administration. Comey served as deputy attorney general from 2003 to 2005 and in March 2004, as acting attorney general, refused to recertify the NSA program. He threatened to resign after President George W. Bush authorized the program without the Justice Department, but reconsidered after Bush agreed to "do the right thing, and put the program on a footing that we could certify its legality." It's unclear how similar the program Comey ultimately approved was to the NSA endeavors revealed in leaks by NSA contractor Edward Snowden earlier this month.