The Puerto Rico Treasury Department has published Circular Letter No. 19-10 of 4 April 2019 concerning quarterly returns for withholding at source (10%) on services rendered using a new quarterly return form, Form 480.6 SP-1. In general, the return is to be filed by the end of the month following each quarter, although the Circular Letter provides that for the first quarter of 2019 ending 31 M…