The U.S.-Portuguese agreement requires each country to issue certificate of coverage
            forms for workers who, without the agreement, would have to pay social security taxes
            to both countries on the same earnings. The certificate serves as proof that the worker
            named on the certificate is:
         
         
            - 
               
                  • 
                     subject to the social security taxation and coverage laws of the country issuing the
                        certificate; and
                      
 
 
- 
               
                  • 
                     exempt from social security coverage and contributions on the same earnings in the
                        other country.