text: Yes they can do a surprise inspection with no notice, but the second part of your question (without reason) is another matter.  OSHA inspections result from worker or public complaints, safety violations you have reported, direct observation by an OSHA employee from nearby property, you are doing work that requires a safety plan that you have submitted, or it is just your turn on the list that they keep.  Many industries such as asbestos workers get inspected routinely as part of OSHA programs.  So they always have a reason, even if it is "just your turn".  You should also document the reason.  They should at least tell you in general.  If not, call the local office.