MONTE CARLO, Monaco - The FIA is not ruling out penalties to follow the stewards' investigation of Mercedes' "secret" Barcelona tyre test.Before the Monaco GP Red Bull and Ferrari filed an official protest, arguing that the three-day test with a 2013-spec car was a breach of the sporting rules.Having conducted an investigation after Sunday's race, the FIA confirmed it knew Pirelli wanted to do the test but only gave a conditional green light in the event "every team is offered the opportunity" to test.'INFLICT PENALTIES'The FIA statement noted: "The FIA received no confirmation that all teams had been given an opportunity to take part in this test.”F1's governing body is not ruling out the intervention now of the International Tribunal, which could "inflict penalties".Mercedes' Niki Lauda, however, told Brazil's O Estado de S.Paulo that the FIA "sent a delegate" to the test and that Charlie Whiting, FIA F1 race director, and Bernie Ecclestone knew about it too.A Pirelli spokesman said Ferrari was invited to test and turned down the offer; Red Bull adviser Helmut Marko said a Red Bull engineer had also been "informally" asked. It is rumoured that Red Bull and Ferrari each declined because they believed the test would have to be done with a two-year old car. Indeed, between Bahrain and China, a Pirelli tyre test took place with a 2010 Ferrari.Red Bull team boss Christian Horner said: “But every team would like an exclusive test with a current car.”Sauber team boss Monisha Kaltenborn told Auto Motor und Sport: "We knew nothing about it (the Mercedes test).” But Mercedes' executive director Toto Wolff denied the team tried to hide the test and dismissed suggestions the German squad used the opportunity to test car developments."There was only 10 days between the request and the test," he said, "which is not enough time to produce any development parts."SORE LOSERS?Mercedes chairman Niki Lauda insisted: "When we were asked to do this,our team boss Ross Brawn called Charlie Whiting and asked if a test was compatible with the sporting regulations. Charlie consulted with the FIA lawyers and gave us the green light. Moreover, Pirelli didn't just ask us, but Red Bull as well."Christian Horner confirmed that Red Bull was asked by Pirelli. "We declined," he said, "because we are of the opinion that such a test violates the regulations."Wolff, however, is livid, particularly as the storm coincided with Nico Rosberg's convincing victory in Monaco. "The term 'sore losers' comes to mind," he was quoted as saying by Speed Week.But the question remains: did Mercedes unfairly benefit from the exclusive test? Multiple World champion Alain Prost: "Impossible to say, but I don't think we can say this win was because of the test. That wouldn't be fair. What is certain is that unauthorised things are not allowed. Only time will tell.”Stay with Wheels24 for the 2013 Formula 1 season – fresh reports every day.