State regulators are investigating whether Uber has illegally jacked up rates with surge pricing in violation of state law — a claim Uber is contesting, saying it has followed the letter of the law.

The incident now under a state spotlight took place during a nor’easter in early March. Gov. Charlie Baker declared a state of emergency March 3-6.

The Department of Public Utilities, which oversees the state’s ride-for-hire app companies, sent Uber a letter last month, kicking off an investigation into the company’s prices during the deadly storm that left large parts of the state without power. It is DPU’s first investigation of the controversial surge-pricing practice.

The letter asks for the company’s fares during the storm and the time immediately beforehand. DPU is also asking for the company’s revenue and number of riders during the storm. The letter also asks for information on any complaints Uber received during the storm. The deadline for Uber to respond to the state is today. Uber declined to say how the company will respond to the letter.

DPU said it sent Uber and other so-called transportation network companies a notice when the state of emergency was declared, telling them to suspend surge pricing. Uber declined to say whether it received the notice.

Uber is disputing the notion its actions were in violation of state law, saying it is not prohibited from surge pricing during states of emergency. The company says the law only keeps it from raising the “base rate” during states of emergency, which it says is separate from surge pricing fees. When surge is active, a rider is charged an additional multiple of the fare, two or 2.5 times, for example, which is listed as a separate add-on to the total bill.

“We are confident we complied with the law and our team was in communication with the DPU during the state of emergency. We look forward to working with regulators on a quick resolution,” an Uber spokesperson said.

The language in the law has been consistently described by lawmakers as a prohibition against surge pricing during states of emergency, but does not define the term “base rate.” States of emergency are not covered in DPU’s regulations.

“The intent was to avoid circumstances where companies would be jacking up prices during a state of emergency,” said state Rep. Aaron Michlewitz, who wrote the original bill. “The intent of the legislation was to avoid any company taking advantage of the consumer during a state of emergency.”

If DPU finds Uber violated the law, the department has the authority to impose fines based on the company’s revenue and has the authority to revoke a company’s license to operate in the state.

The early March storm brought heavy rain and wind across Massachusetts. Hundreds of thousands of homes and businesses were without power, and many coastal communities saw dramatic flooding. The storm led to at least eight deaths in the Northeast.