In both houses of Congress, legislation is initiated to forbid U.S. military support of any South Vietnamese invasion of North Vietnam without congressional approval. This legislation was a result of the controversy that arose after the invasion of Laos by South Vietnamese forces in Operation Lam Son 719. On February 8, South Vietnamese forces had launched a major cross-border operation into Laos to interdict the Ho Chi Minh Trail and destroy the North Vietnamese supply dumps in the area.
Although the only direct U.S. support permitted was long-range cross-border artillery fire from firebases in South Vietnam, fixed-wind air strikes, and 2,600 helicopters to airlift Saigon troops and supplies, President Richard Nixon's critics condemned the invasion. Foreign Relations Committee chairman Senator J. William Fulbright (D-Arkansas) declared the Laotian invasion illegal under the terms of the repeal of the Gulf of Tonkin Resolution, which allowed the president only the mandate to end the war.