WASHINGTON (AP) — Treasury Secretary Janet Yellen notified Congress on Monday that the U.S. could default on its debt as early as June 1, if legislators do not raise or suspend the nation's borrowing authority before then and avert what could potentially become a global financial crisis.

In a letter to House and Senate leaders, Yellen urged congressional leaders "to protect the full faith and credit of the United States by acting as soon as possible" to address the $31.4 trillion limit on its legal borrowing authority. She added that it is impossible to predict with certainty the exact date of...