Every year OSHA puts out their top ten list of violations that they have issued. For 2018, the list includes:

Fall Protection – General Requirements (1926.501): 7,270 violations
Hazard Communication (1910.1200): 4,552
Scaffolding (1926.451): 3,336
Respiratory Protection (1910.134): 3,118
Lockout/Tagout (1910.147): 2,944
Ladders (1926.1053): 2,812
Powered Industrial Trucks (1910.178): 2,294
Fall Protection – Training Requirements (1926.503): 1,982
Machine Guarding