The consumer organisation claims this "valuable information" could be under threat from a Food Standards Agency (FSA) review of administrative costs for manufacturers.
The Which? research sates that currently, labels on meat products that look like cuts, slices and joints of meat must clearly state what ingredients have been added to bulk it up.
A Which? spokesman said: "The FSA, however, is now looking at simplifying meat labelling, despite Which? previously calling for the requirements to be strengthened."
Which? chief policy adviser Sue Davies, said: "This labelling information helps people make informed choices between products. If it's removed, it'll be harder to see from the packet whether you're buying ham that's been bulked up with water, starch or protein."
"Our research indicates most people would be against any change to this regulation and in fact would like to see it go even further."
She added Which? findings included that nine in ten (92%) thought that meat products should show added ingredients on the front of the pack and four in five (80%) were concerned that a wide range of ingredients besides meat were used in meat products.
Sue Davies added: "We think it's outrageous that the FSA is considering doing this and that the motivation for the review is to reduce the burden on industry, rather than to improve consumer information.
"Which? has been concerned that existing labelling information doesn't go far enough, so to us it seems ridiculous to think of reducing it."
A spokeswoman for the Food Standards Agency said: "Consumer protection and consumer confidence are at the heart of what the agency does and this won't change.
"We're at the very early stages of looking at ways to reduce burdens on business while still protecting consumer interests.
"The agency has a completely open mind about what will come out of the review: we haven't counted anything in or out. This Which?
survey will help to inform our review."