Even as the federal government is starting to crack down on companies that hire illegal immigrants, it's been helping those same workers send money home, cheap. Dubbed Directo a Mexico, the Federal Reserve-sponsored service allows customers without Social Security numbers to wire money through the Fed system to Mexico's central bank at little cost. In September, the Fed expanded the remittance program by allowing immigrants, legal or not, to open accounts at participating banks and credit unions in the U.S. or Mexico. About 27,000 transfers are made through the program each month. The program has attracted the attention of conservative...