In a letter from the Department of Buildings' Investigation, Audits and Discipline Unit for the City of New York, Tradesource, supplier of temporary labor, has been warned that sending unlicensed workers to perform plumbing work is illegal. Tradesource was warned that its employees may not perform plumbing or electrical work in New York City and that all Tradesource employees performing such work must stop or Tradesource may face criminal prosecution by the city.