The Frontier Duty Free Association says its members have seen their revenue decline by 60 to 80 per cent because of it. A letter from the association representing duty free stores and a group of 15 border city mayors is also asking for clarity on export rules.

<p>The Frontier Duty Free Association says its members have seen their revenue decline by 60 to 80 per cent because of it.&nbsp;A letter from the association representing duty free stores and a group of 15 border city mayors is also asking for clarity on export rules.</p>