"1. Letters that meet one or more of the nonmachinable
characteristics in DMM 101.1.2 are subject to the $0.20
nonmachinable surcharge.
"2. Large envelope-sized pieces that are rigid, nonrectangular,
or not uniformly thick pay package prices."

A "letter" must meet these standards: between 3.5 and 6.125 inches high; between 5 and 11.5 inches long; maximum thickness 0.25 inch. If it exceeds any of these, it is a large envelope by postal definitions.

A "large envelope" must meet these standards: between 6.125 and 12 inches high; between 11.5 and 15 inches long; maximum thickness 0.75 inch. If it exceeds any of these, it is a package by postal definitions. Writing "do not bend" makes it rigid by definition, and package price must be paid.

At a minimum, a bubble wrap envelope with a chip in it will generally exceed the 0.25 inch maximum thickness and will end up in the large envelope category. If there is more than a 0.25 inch variation in thickness (such as two chips stacked inside), package pricing is required ("not uniformly thick").

A one-ounce large envelope carries a shipping price of 88 cents. 2 ounces = $1.08. Package prices: 1 ounce = $1.71; 2 ounces = same price.

For those who like to read regulations, here is the post office reg on the subject:
http://pe.usps.com/cpim/ftp/manuals/DMM300/101.pdf

Counter clerks don't always read regulations, just like we don't. They often rely on what someone else has told them, just like we do. If this is a constant problem, you need to bring it up with a supervisor and refer them to the specific pages in the manual. They will not take your word for it, just like they don't take mine.