Middlesbrough believe the only appropriate response to the "Spygate" scandal is a sporting punishment that would prevent Southampton from taking part in the Championship play-off final.
Earlier in the week, Southampton were accused of breaching EFL rules after Middlesbrough claimed a member of Southampton staff had spied on one of the club's training sessions before the first leg of their semi-final.
As is known, the Saints secured a place in the play-off final against Hull City thanks to a late goal from Shea Charles, but the match was dominated by controversy surrounding the "Spygate" scandal.
The EFL later released a statement confirming that a disciplinary hearing into the incident would be held no later than May 19.
Meanwhile, Middlesbrough had requested to attend the hearing to present their evidence in person to the EFL's independent disciplinary committee, but this request was refused.
Now, the club has released a strong statement to make its stance clear.
"Middlesbrough FC takes note of the decision of the Disciplinary Committee not to allow the club to intervene in the proceedings brought by the EFL against Southampton FC," the statement said.
"The club regrets this outcome, given that we are directly affected by the matters under review and possess relevant factual evidence regarding the events and their competitive impact," it said.
"The act in question – the observation and filming of our training session before such an important match – touches on the very essence of sporting integrity and fair competition," the statement continues.
"In these circumstances, the only appropriate response is a sporting sanction that would prevent Southampton FC from participating in the Championship play-off final."
The club also added: "We hope that the EFL, as the regulator, will seek such a sanction before the Disciplinary Committee to protect the integrity of the game, safeguard the interests of all member clubs and prevent any future attempts to secure an unfair and unlawful advantage in the race for promotion to the Premier League."
The statement ended with the warning: "The club reserves all legal rights."
A report from the Daily Mail recently published a photograph of the person claimed to be the Southampton staff member who was hiding behind a tree near Middlesbrough's training ground.

According to the report, the person has been identified as William Salt, an intern at the club, who was confronted by Middlesbrough staff after being seen filming.
It is alleged that he sped away from the scene before entering Rockhill Golf Club, owned by Middlesbrough chairman Steve Gibson.
It is also reported that other Championship clubs suspect they have been "spied on" by Southampton and that transactions carried out near their training centers are being examined./Express newspaper/