NEW YORK (CNN/Money) - Qwest Communications International Inc. became the latest company to admit to significant accounting problems, saying it will restate 2000 and 2001 financial results due to $1.16 billion in improperly recorded revenue.

The telecom said Sunday that it is continuing a review of its accounting practices during the period of 1999 to 2001, and that it no longer could provide future earnings guidance.

Shares of Qwest (Q: up $0.03 to $1.53, Research, Estimates) fell about 20 percent early Monday, widening their year-to-date loss to 92 percent.

"Accounting errors were made; they will be corrected and they will be disclosed," Chairman and CEO Richard Notebaert promised in a call with investors. "Internal practices are being, and will continue to be, enhanced."

The company also withdrew its full-year financial guidance while the new management "reassesses the impact of continuing weakness in the telecommunications sector and the regional economy in the company's 14-state local service area, as well as competitive pressure."

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The company said in April that it expected revenue between $18 billion and $18.4 billion, and earnings excluding interest, taxes, depreciation and amortization (EBITDA) of $6.4 billion-to-$6.6 billion.

If that key measure of earnings drops too low, it could cause financing problems for the financially troubled company, which disclosed that it had covenants in some of its debt that require it to not have debt more than four times EBITDA. The company had long-term borrowings of $21.4 billion on its balance sheet as of April 30, its most recent financial report. Its loans also have clauses that could be triggered by a restatement of results. Company executives therefore stressed Monday that they have not restated results yet, only revealed that a restatement was being studied.

It said it would give new earnings guidance when it reports second-quarter results Aug. 8.

Qwest's did not give an estimate of how large the restatement of results would be, although it did say that a preliminary analysis of services provided by third-party telecommunications providers show costs were overstated by $15 million in 2000, but 2001 costs were understated by approximately $113 million. It also said that it is reconsidering its estimate of a $20 billion to $30 billion write-down of goodwill.

"We cannot restate until we complete the analysis," Notebaert said in the conference call. "We do not have the entire package completed. It would be inappropriate to restate, do more analysis, restate again, do more analysis, and restate again."

The accounting problems are just the latest woes for Qwest, which provides local phone service for 14 states stretching from Minnesota to Arizona, as well as a broadband fiber-optic network. The company admitted earlier this month it had been notified it was facing a criminal investigation by the U.S. attorney in Denver, where it is based. The company previously announced it was the subject of probes by the Securities and Exchange Commission and Congress.

Qwest President and Chief Operating Officer Afshin Mohebbi is scheduled to testify Tuesday at a hearing on "Financial turmoil in the telecom marketplace" before the Senate Commerce, Science, and Transportation Committee, along with the CEOs of bankrupt telecoms WorldCom Inc. and Global Crossing Ltd., as well as Michael Powell, chairman of the Federal Communications Commission. Both WorldCom and Global Crossing sought bankruptcy protection in the wake of questions about their accounting practices.

The company said that it will not be able to comply with a new SEC requirement that by Aug. 14 that CEOs and chief financial officers personally vouch for the validity of their company's financial statements, saying they would instead file a report on why they could not vouch for the results. Notebaert said Qwest would like its review to be completed as soon as possible, but said it would likely take "months rather than days."

In addition to optical capacity sales, some equipment sales and transactions involving its directory services also were recorded in error. The company said revenue recognition policies approved by its previous auditor, Arthur Andersen, were improperly applied by the company. The company now uses KPMG as its outside auditor. Chief Financial Officer Oren Shaffer told investors Monday that some of the errors are simply a matter of sales being recognized in the wrong quarter or wrong year, and that it does not appear to be an instance of a deliberate attempt to inflate different measures of earnings.

"This is purely and simply an accounting error," he said. "These things happen. This obviously requires a tightening up in these groups that made errors. It doesn't require anything more than that."

The company named Notebaert to replace Joseph Nacchio as CEO in June. He also replaced Philip Anschutz, the company's largest shareholder, as chairman. The company had been struggling with financial problems, including a downgrade of its debt to below investment grade or "junk bond" status.