The NBA has opened an investigation into the Philadelphia 76ers for possible tampering and early contact centered on the franchise's summer free agency class of James Harden, P.J. Tucker and Danuel House, sources told ESPN on Friday.

One of the central elements of the league's inquiry includes questions on Harden's decision to decline a $47.4 million player option for 2022-23 and take a pay cut on a new two-year, $68 million deal, sources said. Around the league, there have been questions about whether there is already a handshake agreement in place on a future contract -- which would be in violation of collective bargaining rules.

Sixers president of basketball operations Daryl Morey has already begun answering questions from league attorneys, sources said. The investigation is expected to include interviews with team personnel and the organization turning over electronic correspondence and phone records to league investigators. Teams weren't allowed to have conversations with agents or players on free agency deals prior to the opening of free agency at 6 p.m. ET on June 30.

Harden is guaranteed $33 million for the 2022-23 season and holds a player option on 2023-24 that would allow him to become a free agent and negotiate another new deal.

Harden, a 10-time All-Star and six-time first-team All-NBA guard, says he told Morey he wanted to do his part to strengthen the Sixers' roster and give them a better chance to compete for a championship -- and the player option he declined last month could also give the organization flexibility to make deals once the season is underway.

Tucker (three years, $30 million) and House (two years, $8.4 million) agreed to the maximum contracts available to them under the midlevel and biannual extensions. Harden, Tucker and House previously played under Morey with the Houston Rockets.

After investigations last year, the NBA stripped the Chicago Bulls and Miami Heat each a second-round pick for early contact with free agents Lonzo Ball and Kyle Lowry, respectively, in 2021.

The NBA instituted more stringent penalties in such cases in 2019, including raising the maximum fine for teams to $10 million and adding the possibility of suspending team executives, forfeiting draft picks and even voiding contracts. The possibility of the contracts becoming voided is seen as a virtually non-existent threat.

The Milwaukee Bucks were punished with the loss of a 2022 second-round pick for tampering charges in connection with Sacramento Kings restricted free agent Bogdan Bogdanovic in 2021. In handing out that penalty, the NBA took into consideration that the Bucks did not ultimately acquire Bogdanovic, who eventually signed with the Atlanta Hawks.