Philadelphia-area congressman Joe Sestak asked the vice president in an open letter Thursday to disavow an ad that claims Sestak was relieved of duty "for creating a poor command climate."
Biden is scheduled to headline a Friday rally for Specter in northeastern Pennsylvania.
The Specter ad relies on information in a 2005 Navy Times article. Sestak disputes the report's accuracy and accuses Specter of using "Swift Boat"-style tactics. The retired vice admiral accuses says a contingent of veterans will travel to Scranton on Friday to deliver the letter to Biden.