One soft material beneath the seat covers does not comply with U.S. safety standards, company spokesman John Hanson said.
No fires or injuries have been reported, but Toyota can't legally sell cars that don't comply with U.S. safety codes, Hanson said. The company is still totaling how many vehicles are affected, but it will be in the thousands, according to the spokesman.
The stop-sale order could mean trouble for Toyota and its dealers because it covers the company's top-selling vehicles. Dealers can no longer sell certain Camry, Avalon, Sienna and Tacoma models from the 2013 and 2014 model years, as well as Corollas and Tundras from 2014. The Camry, for instance, is the top-selling car in the U.S. with more than 408,000 sales last year.
It depends on how long the repairs will take. Hanson said the company already has a new material that's being installed at factories and will be put in cars that are on dealer lots.
"We don't think it will take long to get the parts and make the changes," Hanson said, without getting more specific.
As for vehicles already on the road, Hanson says Toyota has reported the problem to the U.S. National Highway Traffic Safety Administration, which will decide if the sold vehicles should be recalled. A NHTSA spokesman said he would check into the matter.
"We don't believe that there is a safety issue here because there have been no reports of any problems," Hanson said.
The stop-sale order affects cars and trucks distributed to dealers in the U.S., Canada and Mexico. In addition, some vehicles were exported outside North America, Hanson said.
The problem was discovered by safety regulators in South Korea, who disassembled seats and tested individual fabrics, Hanson said. U.S. safety standards require fabrics to resist flames at a certain rate, but the one fabric didn't meet the standard, Hanson said.
Toyota spokesman Naoki Sumino in Japan said the affected vehicles were sold since August of 2012, when the fabric supplier was changed.
Toyota has been struggling to regain its once sterling reputation for quality after announcing massive recalls over several years, starting in 2009, for a variety of defects including braking, accelerators and floor mats.
The company was fined for being slow on recalls, which affected more than 14 million vehicles, and faces lawsuits.
Toyota, the top automaker ahead of General Motors Corp. and Volkswagen AG in global vehicle sales, has promised to be quicker with recalls and more careful with model development to avoid a recurrence of its troubles.