Senate Commerce, Science and Transportation Committee Chairman John Thune has asked Apple Inc. CEO Tim Cook for details about the company’s slowing of iPhones and handling of consumer complaints.

Apple acknowledged in December it slowed older the performance of older iPhones through a software update to prevent unexpected shutdowns of weakened batteries in various models, including the iPhone 6 and iPhone 6S. The announcement fed years of speculation that Apple slows older phones to drive sales of new models.

Thune’s questions in a Jan. 9 letter, which follow French prosecutors’ announcement that they will conduct a criminal investigation of Apple, turned up the heat on the tech giant despite its discount on new batteries. Apple is also facing at least 34 lawsuits in the U.S. regarding the battery performance slowdown, according to Bloomberg Law data.

Thune (R-S.D.) whose committee oversees consumer protection issues, asked Cook if Apple had considered offering free battery replacements for customers, or rebates to those who had already replaced batteries.

“If Apple’s actions were indeed only intended to avoid unexpected shutdowns in older phones, the large volume of consumer criticism leveled against the company in light of its admission suggests that there should have been better transparency with respect to those practices,” Thune wrote.

Thune also asked how Apple notified customers about battery replacement options and whether it plans to release a similar software update that could slow phone performance in the future.

Thune told Bloomberg TV in an interview Jan. 10 that technology companies need “appropriate oversight.”

An Apple spokesperson did not immediately respond to a Bloomberg Law request for comment.

Apple Dec. 28 issued an apology for the “misunderstanding” about the battery issue. It reduced the price of replacements for out-of-warranty iPhone batteries from $79 to $29, valid until the end of 2018. The company also said it would add phone features for checking the battery condition.

French prosecutors Jan. 5 opened a preliminary investigation in Paris into whether Apple deceived customers and deliberately designed its phones to become obsolete and prompt customers to buy new devices, according to Bloomberg News.

Thune gave Apple a deadline of 5:00 p.m. on Jan. 23 to respond to his questions. He also asked Apple to prepare a briefing for committee staff.

-With assistance from Gaspard Sebag (Bloomberg News)