2 official at the Department of Homeland Security on Thursday strongly denied allegations that he had helped a politically connected company obtain a foreign investor visa, as his nomination got a White House vote of confidence. Republican senators boycotted the hearing on Alejandro Mayorkas' nomination. Mayorkas, director of U.S. Citizenship and Immigration Services, told the Senate Homeland Security and Government Affairs Committee that suggestions of impropriety on the visa matter were "unequivocally false" and that he had overseen the program "based on the law and the facts and nothing else." "I have never, ever in my career exercised undue influence to influence the outcome of a case," he said. I have never based my decisions on who brings a case but rather on the facts and the law. The Associated Press obtained a letter from White House counsel Kathryn Ruemmler to the committee stating that the administration has no concerns about Mayorkas' "suitability" for the post. She said the White House followed standard procedures in checking out Mayorkas for the job and urged the Senate to swiftly confirm him. Mayorkas' nomination hit a snag this week when the AP reported that the Homeland Security Inspector General's Office was investigating his role in helping secure a foreign investor visa for Gulf Coast Funds Management, a company run by former Secretary of State Hillary Rodham Clinton's brother Tony Rodham. The efforts on behalf of Gulf Coast allegedly occurred even after the application had been denied and an appeal rejected. The hearing played out with an empty bank of chairs for the committee's Republicans. Sen. Tom Coburn of Oklahoma, the ranking Republican on the panel, released a statement saying he wouldn't participate 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 Republicans stayed away as well. The committee's chairman, Sen. Thomas Carper, D-Del., acknowledged questions surrounding Mayorkas' qualifications but said it was important to move forward with the hearing to ensure the department has "strong and stable leadership." "At this point in time, we do not have all the facts," Carper said of the investigation. He also said it was his understanding that Mayorkas had not yet been interviewed by the inspector general's office. Despite 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. 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. 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." According to the inspector general'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. Associated Press writers Julie Pace and Stephen Braun contributed to this report.