Dr. Anthony Fauci on Friday declined a request to voluntarily appear before a second Senate panel, opening another front in Republicans’ investigations into the former public health official’s handling of the COVID-19 pandemic.

An attorney for Fauci rejected the request from Sen. Ron Johnson, R-Wis., chairman of the Senate Permanent Subcommittee on Investigations, arguing that compelling Fauci to testify again after his contentious July 29 Senate hearing would "impermissibly harass or degrade Dr. Fauci for political purposes."

Johnson has been conducting a parallel investigation into Fauci and the federal government’s response to COVID-19, including the safety and efficacy of COVID-19 vaccines.

The refusal comes after Republicans on the Senate Homeland Security and Governmental Affairs Committee voted along party lines last week to hold Fauci in contempt of Congress after he invoked his Fifth Amendment right against self-incrimination more than 100 times during the July hearing.

Committee chairman Rand Paul, R-Ky., has sought to send the contempt referral directly to the U.S. Attorney's Office in the District of Columbia, bypassing a full Senate vote.

"It’s a good legal discussion, and we will make those legal points to DOJ in sending the referral over," Paul told Fox News Digital ahead of last week’s contempt vote.

At issue is whether Fauci can invoke the Fifth Amendment after former President Joe Biden issued him a preemptive pardon before leaving office.

Paul has argued that Biden’s pardon removed Fauci’s risk of federal prosecution and therefore undermined his basis for refusing to answer lawmakers’ questions. Fauci and his attorneys have disputed that position.

Paul has spent years investigating Fauci’s role in the government’s response to COVID-19 and has accused the former National Institute of Allergy and Infectious Diseases director of funding "risky" research that led to an alleged lab leak of the COVID-19 virus in China. Paul has repeatedly called for Fauci to be prosecuted.

Johnson’s subcommittee has separately obtained records related to Fauci and the government’s pandemic response. Fox News Digital previously confirmed that the Department of Health and Human Services sent the subcommittee a copy of Fauci’s pandemic-era cellphone.

The broader Homeland Security panel also received more than 1,000 pages of Fauci’s personal diary before his July hearing.

Fox News Digital reached out to Johnson’s office to ask whether he intends to subpoena Fauci following the refusal. Fox News Digital also sought reaction from Paul’s office and asked Fauci attorney David Schertler whether Fauci would comply with a subpoena compelling his testimony.

Fox News Digital's Alex Miller and Elizabeth Elkind contributed to this report.