In this case, it's deceptive. If the packaging used to contain more product, you could reasonably assume the same package would contain the same amount of product. This is shrinkflation. If you're going to raise prices, just do it. Don't try and trick people, because many will notice and get pissed off.
Are you seriously implying that you check the net weight of every single product you ever purchase, especially ones You've purchased regularly in the past?