Hertz, which in May 2020 filed for protection from creditors under the bankruptcy laws, announced a share repurchase program last week.
Buybacks can raise a stock's price by reducing the number of shares in the market.
Last week, the company said it would immediately start the program, in which it would buy back as much as $2 billion of its stock.
In a letter viewed by CNN, Warren wondered why the company was using funds to buy back stock instead of investing in new cars so it could bring down rental-car prices.
"This decision, and other actions taken before and after Hertz's bankruptcy process reveals that the company is happy to reward executives, company insiders, and big shareholders while stiffing consumers with record-high rental car costs and ignoring the recent history that nearly wiped out the company," Warren wrote.
Hertz said the buyback program "allows for ongoing and profitable investment in the business while utilizing moderate balance sheet leverage and facilitating opportunistic share repurchases."
Hertz was hit hard by the Covid-19 pandemic as travel restrictions kneecapped the car-rental industry and travel more broadly. The coronavirus outbreak forced the more than 100-year-old company into bankruptcy proceedings.
Earlier this year, a group of investment firms that eventually included the New York private-equity firm Apollo Global Management (APO) - Get Free Report acquired Hertz, helping the company emerge from bankruptcy in late June 2021.
"You owe your customers and the public an explanation for this $2 billion buyback and whether it is in the best interests of the long-term health of the company and its consumers," Warren's letter said.
Hertz shares at last check were trading 0.8% higher at $26.19,