PHOENIX — After receiving a request from the Rays to do so last week, MLB has unleashed its Department of Investigation to look into whether the Cubs tampered with Joe Maddon while he was still under contract to Tampa Bay, The Post has learned.

It is the Rays’ contention Maddon only opted out of his contract because he was made aware of what the Cubs were willing to offer him should he jump. If that indeed occurred, it would be an infraction of Rule 3(K) of Official Major League Rules, which forbids teams to talk to personnel under contract with another club.

Cubs officials, Maddon and Maddon’s agent, Alan Nero, all previously have denied the matter was discussed until Maddon officially opted out of his deal on Oct. 23. At the General Managers Meetings, both Nero and Rays general manager Matt Silverman refused comment.

Cubs president Theo Epstein, in a statement last month, detailed that the club found out about the opt-out on Oct. 23 and contacted the Commissioner’s Office to confirm the details.

If it is proven the Cubs tampered, they may have to give the Rays some form of compensation, such as a player, draft picks and/or money. It also is possible — especially if any Cubs official lied to MLB investigators — there could be suspensions. The same wing that investigated Alex Rodriguez in the Biogenesis matter is looking into these tampering allegations.

Maddon had one year left on his Rays contract at what is believed to be $2 million. However, he had a stipulation in his pact that if any of the major Tampa Bay officials left, he would receive a two-week window in which he could opt out of the remainder of his contract. He gained that right when general manager Andrew Friedman departed the Rays to take over as Dodgers president.

Maddon and the Rays had initial contract discussions. Maddon initially asked for a three-year deal that would pay him about $12 million — roughly $3 million, $4 million and $5 million per season in sequence. Tampa Bay’s final offer was for three years at $9 million — topping out at around $3.2 million in a season. The Rays never got a counter-offer on that.

Nero has claimed Maddon had a myriad of offers in his free agency — and not just to manage. But it was clear the Cubs were motivated to get him, though they had a manager, Rick Renteria, under contract. They eventually fired Renteria and signed Maddon to a five-year, $25 million contract.