The Mercedes team principal, Toto Wolff, has warned the row over flexible wings in Formula One could end up in the FIA international court of appeal. As the teams took to the streets of Monaco for practice on Thursday there was increasing tension behind the scenes where official protests are being considered. Any protest and subsequent ICA ruling could affect what is already a finely balanced title fight with Mercedes’ Lewis Hamilton leading Red Bull’s Max Verstappen by 14 points. The issue was first raised after the Spanish Grand Prix when Hamilton questioned the advantage Red Bull may have gained from what he described as a “bendy” rear wing. The regulations have banned movable aerodynamic parts for many years. Some teams, however, have looked to exploit the rules by designing a rear wing that flexes under load to reduce drag on straights and increase top speed. Load tests are undertaken to ensure the wings are sufficiently rigid but after Spain the FIA informed the teams it would introduce new tests on 15 June. But that means the current wings can be used in Monte Carlo and crucially at the next round in Baku, a circuit with the highest top speeds of the season. In Monaco there was frustration that the new tests had not been implemented sooner. “It is incomprehensible that in four weeks you can’t stiffen up a rear wing for the track that is most affected by a flexible rear wing,” Wolff said. “Delaying the introduction [of new tests] for whatever reason leaves us in a legal vacuum and leaves the door open for protests. Not only us but probably two other teams that are most affected, maybe more and a protest could end up in the ICA and that is a messy situation.” The Red Bull team principal, Christian Horner, insisted his team have complied with the regulations and his car has passed all the previous tests. But the Ferrari team principal, Mattia Binotto, admitted his team were pushing the rules to their limit and would probably have to adapt their wing to pass the new tests. Horner was bullish in his response, warning it was unfeasible to expect teams to make fundamental changes in short periods of time. “There has to be a lead time, you can’t expect parts to be magicked up overnight,” he said. “The car complies to the regulations that have been there for the last 18 months and then the test has been changed. There has to be a notice period for that.” McLaren’s team principal, Andreas Seidl, echoed Wolff and would also not rule out making a protest. “Where we strongly disagree is the timing of the implementation,” he said. “We hope the FIA shows a very strong hand and it is simply not acceptable because it puts the teams who comply with the regulations at a big disadvantage.” Sergio Pérez topped the timesheets in first practice at Monte Carlo for Red Bull, a tenth up on the Ferrari of Carlos Sainz. Verstappen put his Red Bull in third place with Hamilton in fifth. In the afternoon, meanwhile, Ferrari were very strong. Charles Leclerc was quickest on his home track, with Sainz in second and Hamilton in third.