The SAR Activity Review – Trends, Tips & Issues (October 2000) addresses the cessation of relationship / closure of account as a result of the identification of suspicious activity, as follows:
The closure of a customer account as the result of the identification of suspicious activity is a determination for an organization to make in light of the information available to the organization. A filing of a SAR, on its own, should not be the basis for terminating a customer relationship. Rather, a determination should be made with the knowledge of the facts and circumstances giving rise to the SAR filing, as well as other available information that could tend to impact on such a decision. It may be advisable to include the organization's counsel, as well as other senior staff, in such determinations.
FinCEN’s SAR Activity Review information may be found here: https://www.fincen.gov/sar-activity-review-trends-tips-issues