US Treasury Secretary Yellen, from a letter she has written to Congress
- U.S. Could default as early as June 1 without debt ceiling hike
- Early June timing is based on additional information now available
- Actual date for default could be 'a number of days or weeks later than these estimates'
- Waiting until last minute to raise debt limit can cause serious harm to business and consumer confidence
- Have already seen Treasury's borrowing costs increasing substantially for securities maturing in early June
