Favre, who is on the reserve-retired list, remains property of the Packers, which would leave the quarterback off limits for conversations with coaches or front-office employees of another team. Contacted Wednesday evening, the NFL is not commenting on the tampering allegation.
The tampering charge was first reported by FoxSports.com.
The Packers contend Favre, who has asked the Packers for his release, has been talking with Vikings offensive coordinator Darrell Bevell, who became friends with Favre when he was an assistant coach with the Packers.
The Vikings, according to a source, are expected to contend Bevell may have had conversations with Favre as a friend but had no involvement in discussing a job with the Vikings.
NFL spokesman Greg Aiello said the league had no comment on the report.
Vikings coach Brad Childress has said in recent days the franchise is content with Tarvaris Jackson as its starting quarterback. What the Packers contend is that Favre and Bevell may have discussed Favre coming to the Vikings.
On June 20, Favre, who retired on March 3, called Packers coach Mike McCarthy and told him he had the "itch" to return to the NFL. On Saturday, Packers general manager Ted Thompson said Favre could return to active status on the Packers if he comes out of retirement, but his role would not be determined. During Favre's retirement, Aaron Rodgers has been the Packers' starter.
If the Packers can prove the Vikings tampered with Favre, the Vikings could be subject to fines or a possible loss of a draft choice.
Senior writer John Clayton covers the NFL for ESPN.com. Information from The Associated Press was used in this report.