Even though Congress was not directly involved in FDR's July 1941 decision for sanctions on Japan, there does not seem to have been much congressional opposition to it. In fact, the actions (which it must be remembered were provoked by Japan's insisting on bases in
southern Indochina, portending a further southward drive) don't seem to have been nearly as controversial as some of the steps FDR took against Germany. As Richard Leopold writes in
The Growth of American Foreign Policy, pp. 586-7:
"After June 22, 1941, Roosevelt felt freer to stand firm in Asia. The invasion of Russia took some pressure off England and exposed some strains in the Tripartite Pact. In March, Hitler had been unable to persuade Japan to attack Singapore and unwilling to reveal his own plans. On April 13 Matsuoka signed in Moscow a five-year neutrality treaty that outraged the Nazis, displeased his own government, and contributed to his downfall. Yet this disunity did not preclude a Japanese ultimatum to France on July 12 demanding the right to occupy airfields in southern Indochina and to use Saigon harbor and Camranh Bay for their fleet. Unlike the concessions obtained in June, 1940, these sites could not be justified as vital to the blockade of Chiang Kai-shek. They portended rather a drive south against the Anglo-Dutch possessions.
"This new advance spurred Roosevelt and Hull into action. On July 24, 1941, the President proposed that the United States, England, Japan, and the Netherlands agree to keep hands off Indochina, but the suggestion was not seriously considered. On July 25 the commanders at Hawaii and other Pacific outposts were told that economic sanctions were imminent and that they should take "appropriate precautionary measures." That same day Douglas MacArthur was recalled to active duty and placed in charge of a new Far Eastern force. On July 26 an executive order froze Japanese assets in America, subjected Japanese commercial transactions to government control, and barred Japanese vessels from the Panama Canal. Oil exports were drastically curtailed, and a total ban seemed likely.
"Such was the climax to the trade restrictions begun in June, 1938. Roosevelt's advisers were split. Some felt economic retaliation to be the sole weapon the United States could wield in the Pacific while it was preoccupied in the Atlantic. Others feared that so sweeping an embargo might precipitate the clash it was designed to avert.
Public and congressional opinion were overwhelmingly favorable. There were almost no complaints of executive usurpation or warmongering. [my emphasis--DT] The President knew that the step involved some risk, but he believed that Japan could be checked for a little more time by economic pressure. He was eager to win that respite, since he shared MacArthur's view that the Philippines, long considered indefensible, could now repel a Japanese assault if they had a requisite number of the new type of heavy bombers..."
https://archive.org/details/growthofamerican00inleop/page/586