Washington (CNN) - Congressional Republicans are turning up the heat on the White House about whether someone in the administration may have illegally offered a federal job to Rep. Joe Sestak, if the Pennsylvania Democrat would not challenge Sen. Arlen Specter's bid for re-election.
The seven Republican members of the Senate Judiciary Committee sent a letter to Attorney General Eric Holder Wednesday demanding he appoint a special prosecutor to investigate the allegations, which were first raised by Sestak several months ago.
"These allegations concern what could be a serious breach of the law," said Sen. Jeff Sessions, R-Alabama, the ranking member on the committee. "There has been enough talk regarding this matter; it is time for a thorough and professional investigation."
Neither Sestak nor White House officials have revealed who from the administration spoke to the congressman nor what job might have been offered him. White House aide David Axelrod told CNN's JKUSA Monday the allegations "would constitute a serious breach of the law."
Read the full letter here [pdf]
However he said after the charges were made White House lawyers investigated and determined "the conversations were perfectly appropriate."
"A mere assurance from the White House counsel is plainly not conclusive," Sessions said. "It is time to get to the bottom of this."
"The allegations in the matters are very serious and, if true, suggest a possible violation of various federal criminal laws intended to safeguard our political process from the taint of bribes and political machine manipulation," stated the letter.
"The White House cannot possibly manage an internal investigation of potential criminal misconduct while simultaneously crafting a public narrative to rebut the claim that misconduct occurred," the letter stated.
In addition to Sessions, the letter was signed by Sen. Orrin Hatch of Utah, Sen. Charles Grassley of Iowa, Sen. Jon Kyl of Arizona, Sen. Lindsey Graham of South Carolina, Sen. John Cornyn of Texas, and Sen. Tom Coburn of Oklahoma.
A similar request for a special counsel, made by Rep. Darrel Issa, R-California, was turned down last week by the Department of Justice, according to Issa's office.