APHIS will send you as many labels as you want, so it's really not a big deal. However, if you feel strongly against sending your labels, you can always ask the exporter to use a courier, which doesn't even require it. Be prepared to pay the extra, though, and they still need the copies of your permits.
It depends on the carrier and the materials. Some require the green and yellow label. More than 12 plants will require a label. From a supplemental document from APHIS:
Guidance on the Importation of PPQ-regulated articles through Express Carriers Requiring Green and Yellow Labels (PPQ Form 508)
Mailing of importations through express carriers will involve both an International Air Waybill and a Domestic Air Waybill. You will need to obtain both the International and the Domestic Air Waybills at the initial stage of shipment. The International Air Waybill brings the material into the United States and to the appropriate Plant Inspection Station. It is important to note that the International Air Waybill address for delivery must be the same as the PPQ Label. Otherwise, the shipment may be prohibited or returned to origin. The Domestic Air Waybill ensures delivery from the Plant Inspection Station to the final destination.
Place the Domestic Air Waybill inside the package to be shipped. Upon clearance of the shipment at the Plant Inspection Station, the inspector will attach the Domestic Air Waybill to the package and forward the package to the final destination listed on the Domestic Air Waybill.
Address the International Air Waybill as follows:
o From: Shipper
o To: The Plant Inspection Station Listed on the Green & Yellow Import Label
• See example of import label below
Address the Domestic Air Waybill as follows:
o From: The Plant Inspection Station Listed on the Green and Yellow Import Label
• See example of import label below
o To: Final Address as Outlined on the Permit
For Permitting and Labeling questions, please contact our Customer Support Center at (301) 851-2046. For additional information on the importation of Plants for Planting visit:
http://www.aphis.usda.gov/plant_health/permits/nursery.shtml