Harry Hamburg, AP
In this May 11, 2010 file photo, Immigration Services Director (USCIS) Alejandro Mayorkas listens to a question on Capitol Hill in Washington. Mayorkas, President Barack Obama's choice to be the No. 2 official at the Homeland Security Department is under investigation for his role in helping a company secure an international investor visa for a Chinese executive, The Associated Press has learned.

WASHINGTON — President Barack Obama's pick to be the No. 2 official at the Homeland Security Department faces questioning from lawmakers about an investigation into his role in helping a company run by former Secretary of State Hillary Rodham Clinton's brother secure a foreign investor visa.

Alejandro Mayorkas, the director of U.S. Citizenship and Immigration Services, was to testify Thursday at his confirmation hearing before the Senate Homeland Security and Government Affairs Committee. His nomination hit a snag Tuesday when The Associated Press reported that the Homeland Security Inspector General's Office was investigating Mayorkas' role in helping secure a foreign investor visa for Tony Rodham's Gulf Coast Funds Management even after the application had been denied and an appeal rejected.

Sen. Tom Coburn of Oklahoma, the ranking Republican on the panel, said in a written statement released Thursday that he wouldn't participate in the hearing because it would be unfair to do so until the allegations are resolved and there is no pending investigation.

"We believe the committee must wait until these allegations against Mr. Mayorkas are resolved before deciding whether to move forward with his nomination," Coburn said.

Other Republican senators on the committee were considering following Coburn's lead.

The nomination took on new importance earlier this month when Homeland Security Secretary Janet Napolitano announced she would be leaving the massive department in September to take over as president of the University of California.

Should Mayorkas be approved by the Senate, he almost certainly would lead the department until a permanent replacement for Napolitano is named. With Napolitano's departure, 15 of the department's 45 top positions will either be filled with an acting official or vacant altogether.

Congressional officials briefed on the Mayorkas investigation, who spoke on the condition of anonymity because they were not authorized to release details of the case publicly, said the visa was for a Chinese executive. Homeland Security and Citizenship and Immigration Services have not commented on the investigation.

In an email to lawmakers Monday, the inspector general's office said that "at this point in our investigation, we do not have any findings of criminal misconduct."

Rodham's company said Tuesday it was not aware of the investigation or of any investor visa application being denied.

In a prepared opening statement, the committee's chairman, Sen. Thomas Carper, D-Del., acknowledged questions surrounding "Director Mayorkas' qualifications."

"At this point in time, we do not have all the facts," Carper said. He also said that it's "my understanding" that Mayorkas has not yet been interviewed by the inspector general's office. He added that despite objections from Republicans, including Coburn, "This hearing will allow us to continue the process of vetting this nominee."

Aside from the controversy surrounding Mayorkas, Carper expressed confidence in his nomination.

"I have also taken the opportunity to review Mr. Mayorkas' FBI file, not once, but twice. Nothing in my conversations with Mr. Mayorkas or in my review of his FBI file has convinced me that we should not be holding this hearing today," Carper said.

According to the IG's office email to lawmakers, the FBI's Washington Field Office was told about the Mayorkas investigation in June after it inquired about Mayorkas as part of the White House background investigation for his nomination.

The investigation does not appear to have any direct ties to Clinton's tenure as secretary of state. Nonetheless, any hint of scandal or even the most tangential connection to Clinton, who is a possible 2016 Democratic presidential candidate, is likely to become fodder for Republican super PACs, which have sought to discredit her record while she maintains a lower profile with private speeches and work on a new book.

The international investor visa program run by USCIS, known as EB-5, allows foreigners to get visas if they invest $500,000 to $1 million in projects or businesses that create jobs for U.S. citizens. The amount of the investment required depends on the type of project. Investors who are approved for the program can become legal permanent residents after two years and can later be eligible to become citizens.

Even before the inspector general's investigation became public, two other congressional officials said several Republican members on the committee had planned to ask Mayorkas for more details about his role in the 2001 commutation by President Bill Clinton of the prison sentence of the son of Horacio Vignali, a Democratic Party donor in Los Angeles.

The officials, who spoke on the condition of anonymity to because they were not authorized to comment on the committee's inquiry, said a background questionnaire submitted to Mayorkas in advance of the hearing pressed him for a detailed accounting of his actions in the weeks before the sentence was commuted on Clinton's last day in office.

Another of Hillary Rodham Clinton's brothers, Hugh Rodham, had been hired by Horacio Vignali to lobby for the commutation for his son, Carlos, who was serving a 15-year sentence for his conviction on three federal drug charges.

Mayorkas, who was a U.S. attorney in California at the time, told lawmakers during his 2009 confirmation hearing to head USCIS that "it was a mistake" to have talked to the White House about the request. The congressional officials said Mayorkas acknowledged in recent answers to his questionnaire that he also had telephoned a U.S. attorney in Minnesota at the time to check on the Vignali commutation matter.

The nomination took on new importance earlier this month when Homeland Security Secretary Janet Napolitano announced she would be leaving the department, among the government's largest with 240,00 employees, in September to take over as president of the University of California.

Associated Press writer Stephen Braun contributed to this report. Follow Alicia A. Caldwell on Twitter at www.twitter.com/acaldwellap