THE Trade Department has asked for deferral of Mexico's new rules on origin of imports and certification requirements which are expected to damage trade between the two places. The trading authorities yesterday sent another letter to the Mexican Government reiterating Hong Kong's concerns over the new certificate of origin requirements and requesting a further postponement of their implementation. On May 31, Mexico announced the new regulations for merchandise imports that were subject to anti-dumping or countervailing duties. The certification requirements had initially been scheduled to come into force on July 15, but were deferred to September 1. Deputy Director-General of Trade Thomas Yiu said the Mexican Government had promised to publish modifications to the requirements and had supplied some advance information. However, some of the modifications were unclear, and the requirement as modified were still problematic. ''One purpose of our letter is to seek clarification. We also reiterated our request for the September 1 implementation to be deferred,'' said Mr Yiu. ''This deferral is all the more necessary now that the Mexican Government is going to announce modifications. They must surely allow time for other governments to study the modified arrangements and to seek clarification and consultation if necessary. ''We fully recognise the undesirable effect on trade which may be created by any uncertainty. But, we must bear in mind the wider, long-term interests of Hong Kong's trade with Mexico.''