No and if they catch it they will delivery it postage due priority.  You can only reuse it if you are going to send priority again.

My post office told me as long as they had been used once as priority, I could then turn them inside out an recycle them.

I got a package for something I bought on ebay and the postman left a note saying I owed extra postage.  In contacting the seller, he said his P.O. said it was ok but it I believe it says on USPS webpage NOT to reuse that it is a violation of the law.  Better check it out, I wouldn't do it if it was me.  The sender I worked with got very nasty with me about it so I would err on the side of caution so you don't end up leaving the receipient to sort it out on their end.

Be prepared to have a book sent back or to offer credits to the recipient if it arrives postage due.  If I had a book arrive to me postage due for priority I would refuse it and send it back.

The USPS's position is that the Priority Mail envelopes remain the property of the USPS and they may not be used for anything other than Priority mail.  By their rules you can not even use a used Priority Mail envelope to line the bottom of your bird cage.

So instead we receive the envelopes with postage already paid and then are forced to turn around and toss the envelope in the trash? What a waste--how un-green!! Filling up landfills with materials that will live hundreds of years undegraded.

Frankly, I've reused them for wrapping and have had no problems as long as they are inside out and no hint of the priority printing shows through. If it does, cover it with your PBS label. Just never use an unused priority envelope--that's cheating the USPS, and who would want to do that? LOL!!

Well like I said-be prepared to cover the postage if they catch you. I just put them in the recycling.  Not worth the trouble if you get caught.

So instead we receive the envelopes with postage already paid and then are forced to turn around and toss the envelope in the trash? What a waste--how un-green!! Filling up landfills with materials that will live hundreds of years undegraded.

 No, you can reuse the envelopes and not toss them, you just have to reuse them for the same class of mail. They encourage recycling, just doing it within their regulations.

Frankly, I've reused them for wrapping and have had no problems as long as they are inside out and no hint of the priority printing shows through. If it does, cover it with your PBS label. Just never use an unused priority envelope--that's cheating the USPS, and who would want to do that? LOL!!

This will not work with new envelopes because they have markings on the inside to and they WILL mark the package up to the class of mail the packaging is for. Regardless of the USPS stance on it (which is that it is illegal), PBS rules clearly state you should not be using it for PBS packages.

Poor choices for alternate packaging materials:

The Post Office randomly checks media mail to see if the contents qualify for the media rate. It can be checked anywhere along the way and many of the priority packages are a unique shape that I would set aside for inspection. If your package is selected to be checked, it will be sent on postage due. If the person refuses to pay the postage, it will come back to you still postage due. You can reuse priority packaging sending priority mail. If you have extra priority packaging, freecycle it or give it back to the Post Office.