The group of money managers and pension experts are now calling on the government for stricter takeover guidelines, Reuters reports.
Recently-announced proposals from pulp producer Votorantim Celulose e Papel (VCP) to take over smaller rival Aracruz Celulose have sparked the ire of firms including F&C Asset Management, TIAA-CREF and Legg-Mason.
One of the group's key complaints is that such acquisitions make the Brazilian market less appealing for overseas investors who wish to buy minority stakes in companies.
Urban Larson at F&C Asset explained: "We are worried about the potential effect this could have in the Brazilian market as a whole since it does affect investors' perception as to how minority shareholders will be treated."
Commenting on the situation Luiz Leonardo Cantidiano, a lawyer for VCP, said: "Brazilian regulations are good because they are clear.
"If investors want more rights, they should look for a market that guarantees that."