Page "Article Two of the United States Constitution" Paragraph 41

The President may call extraordinary sessions of one or both Houses of Congress.

If the two Houses cannot agree on a date for adjournment, the President may adjourn both Houses to such a time as befits the circumstances.

The last time this power was exercised was in 1948, when President Harry S. Truman called a special session of Congress.

That was the twenty-seventh time in American history when a president convened such a session.