An aide to former Republican Sen. John Ensign pleaded guilty Thursday to a misdemeanor violation of a law that prohibits congressional aides from lobbying for at least a year after leaving a job.

Doug Hampton, Ensign's former administrative assistant, had originally been charged with seven felony counts of violating a one-year ban on former staffers lobbying the Senate. Under terms of the agreement, prosecutors will argue for a sentence somewhere between no jail time and six months as well as a fine ranging from $250 to $5,000.

Hampton, 50, had resigned his job four years ago after learning that his wife and Ensign were having an affair. He lobbied the Nevada Republican's office just a few days after leaving on behalf of Allegiant Air, an airline service headquartered in Las Vegas.

Documents filed in U.S. District Court on Thursday state that Hampton told an aide in Ensign's office the airline wanted the Department of Transportation to reconsider its stance on a fuel surcharge and requested the aide or Ensign to help resolve the issue. Hampton also told the aide that Allegiant Air would suffer significant financial harm if the issue were not adequately resolved. The documents, which Hampton signed, stated that Hampton knew he was prohibited from making such communications because of the one-year lobbying ban for former Senate employees.

U.S. District Judge Beryl Howell made clear to Hampton that she didn't have to accept the terms of the plea agreement. She could sentence him to up to one year in prison and a $100,000 fine. Hampton said he understood. Hampton's attorney, A.J. Kramer, told Howell that he would argue for no jail time.

A sentencing hearing was set for Sept. 5.

Ensign resigned last year as the Senate Ethics Committee was concluding its investigation of the senator's conduct as he sought to conceal the affair. The committee issued a scathing report that called for investigations from the Justice Department and the Federal Election Commission.

Ensign apologized for his conduct while serving in the Senate, but he and his attorneys consistently rejected the notion that he violated any laws or Senate rules. Ensign has not been charged with any wrongdoing.

Both Hampton and his attorney declined to speak with reporters after the hearing.