A member of the Saints' staff was photographed at the Middlesbrough training ground ahead of the two sides' 0-0 first leg play-off draw last week.
It is alleged the Southampton representative was spying on Middlesbrough in an attempt to gain a competitive advantage ahead of the two-legged affair.
An individual, purported to be a Saints analyst - which is a cornerstone of Boro's case - was spotted overlooking the training pitches at Rockliffe Hall, a public-access golf and hotel resort where the north-east club train.
Southampton face play-off final ban for SPYING
The suspect was reportedly filming the session on a mobile device and using headphones, leading to suspicions they were live-streaming information back to Southampton’s staff.
According to The Times, the south coast club could now face a sporting sanction, by way of a points deduction next season, or even expulsion from the play-offs, if found guilty of the spying charges.
Middlesbrough boss Kim Hellberg described the incident as 'cheating' and the club have lodged an official complaint with the EFL, calling on Southampton to be hit with the strongest possible punishment.
The two teams meet this evening at St. Mary's Stadium, vying for a place in the Play-Off Final against Hull City, who were 2-0 aggregate winners over Millwall in the other semi-final on Monday night.
In 2018, Leeds United were accused of a similar offence, with then-boss Marcelo Bielsa admitting a member of club staff had been instructed to spy on play-off semi-final opponents Derby County.
The Argentine coach paid the resulting fine out of his own pocket, taking full responsibility for the incident in a lengthy and spectacular press conference in which he outlined the depth of his team's preparations for the match.
Southampton have been charged with a breach of Regulation 3.4 and Regulation 127, the latter of which was established following the original 'Spygate' incident. The former pertains to member clubs acting toward each other in 'good faith'.
Regulation 127 strictly forbids opposition sides observing the other team's training within 72 hours of a match.
It is suggested Southampton may argue the analyst acted independently to prove his worth, rather than under official instruction.
Boro plan to continue training even if they are eliminated tonight, believing an independent commission could still disqualify Southampton and reinstate the Teesiders for the Wembley finale on May 23.
A date for the hearing is yet to be announced by the EFL, leaving the most lucrative game in world football clouded in controversy.
