Poly bagging... is it a hard requirement?

I sell items on amazon which are vacuum sealed in their original packets and then put into poly bags and the amazon prime label attached on the outside

I’ve recently ordered some products from similar sellers and have found that they do not poly bag the items, other than that our packaging is the same, the other sellers simply attach the amazon barcode to the back of their packaging bag like this for example: https://www.amazon.co.uk/Alpha-GPC-99-Powder-Concentration/dp/B078YYHQF9/ref=sr_1_7_a_it?ie=UTF8&qid=1551772867&sr=8-7&keywords=alpha+gpc

Please can you tell me, is it a REQUIREMENT to put the item (similar to that linked above) into a plastic bag after it is already packed?

Its not really a big problem but it does add to the size of my shipment and I feel bad using all those extra plastic bags if its not necessary from an eco point of view.

Thanks in advance for any advise given.