Roughly, if you deposit more than 10K USD in cash, they will need to file this form with the OCC. And, a bunch of other activities qualify. There is no guarantee that this will result in account closure, not does it directly indicate illegal activity. This seems to be a myth online. In the industry, the SAR is regarded as a "get of jail free card" for poorly staffed compliance departments. "When in doubt, file a SAR!", then the bank cannot be so easily sanctioned for allowing illicit activities.