The FA said in a statement:
"The commission found that Mr. Stretford did encourage Mr. Rooney and his parents to enter into a representation agreement with Proactive Sports Management Limited on July 17, 2002, although he knew Mr. Rooney was still then under contract with Pro-Form Sports Management Limited."
Reuters reported that Streford will appeal.
"I will be lodging an immediate appeal against the verdicts and continue to maintain my complete innocence of the charges brought against me," Stretford said.
Stretford became Rooney's agent in September 2002 and Rooney transfered from Everton to Manchester United two years later.
If Stretford is found not to have broken further regulations he will only serve half of the suspension.
The FA stated that Stretford had signed Rooney to an eight-year contract, despite the limit being two years and that he had failed to lodge representation contracts with the FA.