Romain Grosjean was disqualified from the Italian Grand Prix because Haas knowingly used a floor design on its Formula 1 car already deemed illegal by the FIA's technical department.
The FIA stewards deemed Grosjean's floor contravened Article 3.7.1.d of the technical regulations or a technical directive (TD) published before the summer break.
Their detailed report of the decision explained Haas had already notified by the FIA that its design would be illegal.
The FIA article states "the surface formed by all parts lying on the reference plane must have a 50mm radius (+/-2mm) on each front corner when viewed from directly beneath the car, this being applied after the surface has been defined".
However, it issued a TD on July 25 because the article was "being applied differently by several different teams" and gave competitors until this weekend's Monza race to comply with the clarification.
Haas told the stewards that it understood the TD and discussed it with the FIA's head of single-seater technical matters Nikolas Tombazis.
The stewards heard that Haas, in an email, had stated: "Given the forthcoming summer break, we will endeavor to introduce this upgrade for the Singapore GP, but will be somewhat at the mercy of our suppliers so we would request some flexibility in this matter."
This was not responded to by Tombazis, who made "some technical points along with general acceptance of the technical solution", which Haas took to mean both its solution and timing had been accepted.
However, Tombazis said that in a subsequent conversation with Haas head of aerodynamics Ben Agathangelou he had stated he understood their supply problem but if the car was not corrected by Monza then Haas would leave itself open to protest by other teams.
Renault duly lodged its protest after the Italian GP, in which Grosjean finished sixth to take Haas above Renault into fourth in the constructors' championship.
The stewards reconvened their hearing after Haas asked to be heard on additional points.
The team noted that in his email to the FIA, Agathangelou had proposed a solution as a result of discussions on how to interpret the ambiguity with defining the front of the T-Tray, the area in question.
Haas considered this notice that until the clarification was given, the TD was ambiguous and therefore the car was not in violation of it.
The hearing was closed again, and the stewards upheld the technical delegate's report of the car - issued following Renault's protest - that it was not in compliance.
The stewards acknowledged that TDs are "advisory in nature but provide a manner in which a competitor may satisfy the technical delegates and the stewards with proof that their car is compliant".
In this case, Haas did not follow the TD.
The stewards said they were "sympathetic to the difficulties of producing these parts" but said at least one rival team complied with the TD in the same timeframe.
They also said it was "made clear" to Haas "from the outset" that the FIA's technical department did not consider the car to be in compliance, and therefore Haas left itself open to protest.
Grosjean was duly disqualified from the results, while the part in question has been retained and sealed by the technical delegate until the stewards' decision is "binding".
Haas has notified the FIA of its intention to appeal.
Team principal Gunther Steiner said in a statement: "We do not agree with the Stewards' decision to penalise our race team and we feel strongly that our sixth-place finish in the Italian Grand Prix should stand. We are appealing the Stewards' decision."
As well as promoting Renault back to fourth in the championship, Grosjean's exclusion elevates Sergey Sirotkin to 10th and means the Williams rookie scores his first point of the season.