Commission Regulation (EC) No 1683/1999 of 28 July 1999 initiating an investigation concerning the alleged circumvention of anti-dumping measures imposed by Council Regulation (EC) No 584/96 on imports of certain tube and pipe fittings of iron or steel originating in the People's Republic of China by imports of the same tube and pipe fittings of iron or steel transhipped through Taiwan, and making such imports subject to registration