Who: Immigration Quota Act, or The Immigration Act of 1924, or Johnson–Reed Act (including the National Origins Act, and Asian Exclusion Act)
At the time Coolidge was president, he became president after Harding. They both supported isolationism after WW1.
When: enacted May 26, 1924
Where: Was a US federal law that cut quotas (limited number of immigrants who could be admitted from any country) for foreigners from 3 % to 2% of the total number of immigrants. The 3% cap was set by the Emergency Quota Act of 1921, which used the Census of 1910.
What: The law was primarily aimed at further restricting immigration of Southern Europeans and Eastern Europeans, especially Italians and Eastern European Jews. In addition, it severely restricted the immigration of Africans and outright banned the immigration of Arabs and Asians.