Let me start by saying, this is not an April Fool’s joke unfortunately…
As of April 1, 2015, any foreign national residing in Argentina for more than 90 days will be required to present a CUIL or CUIT in order to pick up money from any of the money transfer services (Xoom, Azimo, Ria, etc.). This does not apply if your last date of entry into Argentina is less than 90 days ago.
As many expats live here illegally by overstaying their tourist visa and simply pay the $600 peso overstay fee when they leave, this will have an immediate effect on their ability to get money into the country through these services. That 90 day trip to Colonia for a new visa stamp might make a lot more sense now, even if it does expose you to additional scrutiny at the border.
To get a CUIL (Código Único de Identificación Laboral) or CUIT (Clave Única de Identificación Tributaria), you have to have a DNI (Documento Nacional de Identidad). And, to get a DNI, you have to be a legal resident.
UPDATE: Some people are reporting that as of April 20, 2015, Xoom is not asking anyone to provide a CUIL.