( CNN ) Vincenzo Nibali 's defense of his Tour de France crown is in doubt after the UCI requested Friday that the Italian 's Astana team has its WorldTour license withdrawn . Five Astana riders from the Kazakhstan-based team have been caught doping since last August and as a result it had only been granted a provisional license for the 2015 season . The world governing body said in a statement that an audit of the team , carried out by the Institute of Sport Sciences at the University of Lausanne ( ISSUL ) , had given them `` compelling grounds '' to make its decision . `` The UCI considers that the ISSUL audit has , among other things , revealed a big difference between the policies and structures that the team presented to the Licence Commission in December and the reality on the ground , '' it said . Astana has also been caught up in the Padova investigation by Italian police into links between professional cyclists and banned doctor Michele Ferrari , who was Lance Armstrong 's personal trainer . The UCI revealed Friday that some of the evidence it had been provided with by the Italian authorities `` concerns Astana Pro Team members '' and this will also be passed on to its License Commission , which is an independent four-man body , headed by a Swiss judge . Astana has still to make a formal response to the UCI decision , but if it is stripped of its license to race at the highest level of professional cycling it would be a serious blow to Nibali and other star riders like Italian Fabio Aru . A WorldTour license gives an automatic passport to the top races in cycling like the Tour de France , the Giro d'italia and the Vuelta a Espana , plus one-day classics such as Paris-Roubaix and Milan-San Remo . Nibali -- who has never failed a drugs test -- would be forced to switch to another team if he wants to compete , assuming his current contract with Astana has a get out clause . The 30-year-old Nibali captured the coveted yellow jersey of the Tour de France last July -- succeeding Team Sky 's Chris Froome , who crashed out in the early stages of the 2014 edition . Astana , the team self-confessed drugs cheat Armstrong chose to ride for in his 2009 comeback , has a controversial past and is headed by Kazakh Alexander Vinokourov , who served a two-year ban after being caught doping at the 2007 Tour de France . The latest scandals involved brothers Maxim and Valentin Iglinskiy , who were caught using the blood-booster ( EPO ) , while three riders from its development squad also failed drugs tests . It led to widespread calls for the UCI , under the new leadership of Briton Brian Cookson , to take firm action and Astana was only granted its temporary license under condition that its management and anti-doping policies would face further scrutiny . Back in 2012 , the UCI stripped Katusha of its WorldTour license , but the Russian-based team successfully appealed to the Court of Arbitration in Sport to be reinstated .
UCI wants Lance Armstrong 's WorldTour license withdrawn . four Astana winner Vincenzo Nibal rides for Astana . World governing body voices concerns over team 's anti-doping policies . Lance Armstrong rode for Astana in 2014 .