From the Document: "On April 22, President Trump issued a proclamation suspending entry into the United States of certain aliens (foreign nationals) who are seeking lawful permanent resident (LPR) status (i.e., immigrants). The President justified the suspension as needed to protect American workers from foreign labor force competition during a time of 'high domestic unemployment and reduced demand for labor' caused by the coronavirus pandemic. The President cited two immigration-related legal authorities. Under Section 212(f) (8 U.S.C. §1182(f)) of the Immigration and Nationality Act (INA), the President may suspend immigration when it would be detrimental to the interests of the United States. Under INA 215(a) (§8 U.S.C. §1185(a)) the President may prescribe limitations and exceptions on who may enter or depart the United States."
CRS Insight, IN11362
Congressional Research Service: https://crsreports.congress.gov/