Working in Romania is possible only with a valid work permit issued by the Ministry of Labor & Social Protection (www.mmuncii.ro; Romanian only) and in conjunction with a Romanian employer. The procedure for obtaining a permit should be initiated before arriving. Working in Romania also normally requires a long-stay visa. The website of the Romanian Ministry for Foreign Affairs (www.mae.ro) has information in English on steps for obtaining such a visa.
Just Landed (www.justlanded.com) is a helpful resource for sorting out the bureaucracy and getting started.