(Adds details from letter)
WASHINGTON, April 8 (Reuters) - The National Highway Traffic Safety Administration said on Tuesday it was fining General Motors $7,000 a day for missing an April 3 deadline to respond to the U.S. agency's request for information about the automaker's recall of 2.6 million cars for defective ignition switches.
In a letter to GM, NHTSA said the automaker had so far been fined $28,000 and would be subject to additional daily fines until it answers all 107 questions the agency asked as part of its investigation into why the automaker waited until February to order a recall despite first learning of the defect more than 10 years ago.
At least 13 deaths have been linked to the faulty ignition switches, which can cause the engine to turn off suddenly, disabling the air bags and making steering and braking more difficult.
GM said in a statement it had "fully cooperated" with NHTSA. The automaker said it had sent more than 271,000 pages of documents to the agency and would provide additional documents "as soon as they become available."
The automaker had not responded to over a third of NHTSA's questions by the April 3 deadline, the agency said. The 17 pages of questions were submitted to GM on March 4.
NHTSA said GM had informed the agency on March 20 it would not be able to respond to all the technical engineering questions by the deadline.
"NHTSA had no objection to GM taking additional time to respond to technical engineering questions, with the understanding that GM would fully respond to the remaining requests by the April 3 deadline. GM failed to do so," NHTSA Chief Counsel O. Kevin Vincent said in the letter.
NHTSA said GM had also told the agency it was not able to respond fully because of an investigation into the recall by former federal prosecutor Anton Valukas, who has been hired by GM.
Vincent said if GM did not fully respond to NHTSA's questions "immediately and pay all civil penalties," the agency may refer the matter to the Justice Department.
(Reporting by Eric Beech; Editing by Sandra Maler and Peter Cooney)