Hamilton has won five Formula One races
Sir Jackie Stewart says Lewis Hamilton is "completely wrong" not to join the Grand Prix Drivers' Association.
The McLaren driver, who won the opening race of the season in Australia, claims he has not joined the union because he has "so much going on".
But former world champion Stewart believes every driver should support the union's attempts to improve safety.
"I'm surprised and disappointed. He has been badly advised," he said. "It is completely wrong not to be involved."
Stewart was instrumental in changing the sport's attitude to driver safety, both during his career and after.
The GPDA was formed in 1961 but it was thanks to Stewart's tireless campaigning during the 1960s and '70s that the association became influential, introducing fireproof overalls, effective helmets and emergency medical facilities.
There have been no deaths in Formula One since that of Ayrton Senna nearly 14 years ago, but Stewart is concerned that drivers such as Hamilton and world champion Kimi Raikkonen, who is also not a member of the GPDA, are becoming complacent.
"So far we have been incredibly lucky," added Stewart, who won the world title in 1969, 1971 and 1973.
"We are on the slate to have a big shunt. But what is going to happen is this - somebody is going to get killed.
Stewart won the world title in 1969, 1971 and 1973
"At the speeds modern cars do, it'll be like an air crash."
The association's members pay a £2,000 joining fee and attend one 20-minute meeting at the start of each Grand Prix weekend.
When asked in Melbourne why he had not joined the association, Hamilton said: "I had so much going on last year and the same is true now.
"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."
Williams driver Nico Rosberg admitted safety was a concern ahead of Formula One's first floodlit race.
Drivers will race through the city streets of Singapore during the evening of 28 September.
The German said: "Safety is always a concern for street races, and that plus being under the floodlights at night, safety is a bit of a question mark.
"I'm sure the FIA (Formula One's governing body) has done its job and I think it'll be a great event."
Rosberg, who finished a career-best third in Melbourne, said he did not know how he would approach the race.
"I couldn't tell you because I've never driven at night," he said.
"I've never tested. There's no tracks with lights so you can't really prepare."