In response to the military coup in Burma, the U.S. Department of Commerce's Bureau of Industry and Security (BIS) is enforcing tougher export controls on sensitive goods sent to Burma's military and security services. Effective immediately, BIS will mostly deny licenses for exporting or reexporting certain items to Burmese defense and security sectors. Additionally, they have suspended some previously available export license exceptions for items going to Burma. This action aims to hold those responsible for the coup accountable.
Simple Explanation
The U.S. is trying to make sure that Burma's military doesn't get special items they need by making new rules that make it very hard to send those items to Burma. This is because the military took control of the government in a way that was unfair.