Treasury Secretary Timothy Geithner sent a warning letter to Congress Monday, advising legislators that a failure to increase the nation's borrowing authority – or debt ceiling – would lead to "irreparable harm to the American economy and the livelihood of Americans."

The letter addressed to House Speaker John Boehner says the Treasury's extraordinary measures for ensuring the nation doesn't default on its debt obligations expire sometime between mid-February to early March.

To ensure the nation does not default on its debt, the borrowing limit will have to be raised within the next several weeks to avoid a dramatic impact on payments from Social Security, Medicare, Medicaid and other military and government expenses.

"If Congress does not act to extend borrowing authority, all of these payments would be at risk," Geithner wrote in his letter. "This would impose severe economic hardship on millions of individuals and businesses across the country."

Click here to read the full letter.