Those against Amendment 1 hosted a public forum at the East Hills Library.
Members of Missouri's Food for America say if the amendment passes, family farms would suffer.
They say the language is vague and would give foreign corporations an open door to extract wealth from Missouri.
The controversial amendment is aimed at restricting the regulations that can be placed on the agriculture industry in the state.
"This Amendment 1 is an example of how far these big corporations are willing to go to dig their way," said farmer Mike Callicrate.
"Farming's changing and to enshrine in our constitution forever more that someone's right to do with what they want on their land be danged to neighbors and be danged to consumers, I think, is a very dangerous path to go down," said Wes Shoemyer with Missouri's Food for America.
The proposal, which will appear on the August 5 ballot, states any regulations would have to be proven to be for the good of the state.
Supporters, including Missouri Attorney General Chris Koster, say out-of-state regulations could damage the state's top industry.