The Justice Department is investigating whether Republican Rep. Curt Weldon of Pennsylvania traded his political influence for lucrative lobbying and consulting contracts for his daughter, according to sources with direct knowledge of the inquiry.

The FBI, which opened an investigation in recent months, has formally referred the matter to the department's Public Integrity Section for additional scrutiny. At issue are Weldon's efforts between 2002 and 2004 to aid two Russian companies and two Serbian brothers with ties to strongman Slobodan Milosevic, a federal law enforcement official said.