From the Summary: "Currently in the United States, almost 1 million lawfully present foreign workers and their family members have been approved for, and are waiting to receive, lawful permanent resident (LPR) status (a 'green card'). This employment-based backlog is projected to double by FY2030. It exists because the number of foreign workers whom U.S. employers sponsor for green cards each year exceeds the annual statutory green card allocation. In addition to this numerical limit, a statutory 7% per-country ceiling prevents the monopolization of employment-based green cards by a few countries."
CRS Report for Congress, R46291
Congressional Research Service: https://crsreports.congress.gov/