TL;DR: The Chinese Exclusion Act was the first federal law implemented to prevent the immigration of a specific ethnic group into the U.S.

That being said, animosity towards Chinese immigration began in California almost as soon as the Gold Rush began. However, in the early 1850s, there was enough resistance to the excluding Chinese migrant workers from immigration, because of the tax revenue they provided, which helped fill California's fiscal gap. Towards the end of the decade, California's financial situation improved and subsequently, attempts to legislate Chinese exclusion became successful on the state level. In 1858, the California Legislature passed a law that made it illegal for any person "of the Chinese or Mongolian races" to enter the state; however, this law was struck down by an unpublished opinion of the State Supreme Court in 1862. The Chinese immigrant workers provided cheap labor and did not use any of the government infrastructure (e.g. schools, hospitals, etc.) because the Chinese migrant population was predominantly made up of healthy male adults. As time passed and more and more Chinese migrants arrived in California, violence would often break out in cities such as Los Angeles. By 1878 Congress decided to act and passed legislation excluding the Chinese, but this was vetoed by President Rutherford B. Hayes. In 1879, California adopted a new Constitution, which explicitly authorized the state government to determine which individuals were allowed to reside in the state, and banned the Chinese from employment by corporations and state, county or municipal governments. Once the Chinese Exclusion Act was passed in 1882, California went further by passing various laws that were later held to be unconstitutional.

Source: Kanazawa, Mark. "Immigration, Exclusion, and Taxation: Anti-Chinese Legislation in Gold Rush California". The Journal of Economic History, Vol. 65, No. 3 (Sep., 2005), pp. 779–805. Published by: Cambridge University Press on behalf of the Economic History Association.