Takata Corp. boosted spending on U.S. federal lobbying by 22 percent in the second quarter as it faced increased attention from regulators and lawmakers about faulty air bags behind the auto industry's largest recall in history.

The Japanese auto parts-maker paid $390,000 (¥48.5 million) to Squire Patton Boggs to represent it before Congress, the National Highway Traffic Safety Administration and Department of Transportation on "issues relating to air bag safety," according to records filed last month with the U.S. Senate.

That compares to $300,000 in the first quarter spent with Squire Patton Boggs and $20,000 a subsidiary called Takata Protection Systems spent with Washington Alliance Group, according to the filings.

Takata hired Squire Patton Boggs in December and dropped Washington Alliance in the second quarter. Former Transportation Secretary Rodney Slater was one of the Squire Patton Boggs lobbyists listed during the past quarter. A Takata representative declined to comment on the lobbying efforts.

U.S. lawmakers have held four hearings this year to grill the company over the defective devices, which can rupture during deployment and continue to take a toll on customers such as Honda Motor Co., which expanded its recalls in July to 24.5 million vehicles.

Takata has said its air bags have killed eight and injured about 130 people. The supplier, automakers and the National Highway Traffic Safety Administration are still investigating the root cause that explains why the air bag inflators are prone to break apart, spraying metal and plastic components at occupants.

A Senate report released before Takata's latest U.S. hearing in June found that the company's employees knew of serious safety and quality control issues as early as 2001.