The company has received an informal request from the SEC to present its financial documents from 2000 and 2001 for investigation.
The investigation covers two main issues: how Qwest recognised revenue and accounted for sales of optical capacity; and sales of telecommunication equipment to customers who either purchased Internet services from Qwest or who received financing from the company.
This latest inquiry is the second this year, and it comes as the US government is increasing its efforts to police accounting practices in the wake of the Enron and Global Crossing bankruptcies.
Qwest was ordered in early February to turn over documents relating to the purchase of some assets of Global Crossing.
Qwest said in a statement that it intends to respond fully to the SEC's request. The company added that the investigation is preliminary and Qwest has not been found to have violated any laws.
Qwest claimed that its accounting practices "comply with all applicable requirements".