Materials with stretching or shrinking capabilities will often require the barcode to be printed side-ways on your packaging. Exposing the barcode to horizontal scaling can compromise scanning.
Print suppliers will make you sign forms if you require your barcode to have a less than optimal orientation. This will put the responsibility on your shoulders if you have scanning issues down the road. More often than not, this design choice is not worth the risk.
Maximise your chance of success and do it right the first time.