Hamilton under no pressure to join drivers' union

De la Rosa told autosport.com: "Speaking as chairman of the GPDA, I can say that the GPDA respects Lewis Hamilton and the three other F1 race drivers who aren't members of the GPDA - Kimi Raikkonen, Anthony Davidson and Adrian Sutil."

   Former F1 world champion Sir Jackie Stewart said this week Hamilton was "completely wrong" not to join the Grand Prix Drivers' Association.

 The McLaren driver, who won the opening race of the season in Australia, said he had not joined the association because he has "so much going on."

   Both during and after his career, Stewart has been a strong campaigner for driver safety and said Tuesday he was "surprised and disappointed" that Hamilton had not joined the GPDA.

 The association was formed in 1961 and speaks to Formula One's governing body on safety and other issues.

 "Clearly, we look forward to Lewis becoming a GPDA member at some time in the future, and the other three too," de la Rosa said.

 "But it isn't mandatory to join and it isn't our intention to put pressure on Lewis, as he has always been extremely helpful with any safety issue we have engaged in in the past."

   In Melbourne, Hamilton said: "If you're part of an important organisation you have to be committed and I really don't have time for that at the moment."