Blackrock and other asset management institutions are seeking an injunction this week to block the sale of Portugal's Novo Banco to U.S. private equity firm Lone Star.
"The rules governing the sales process are discriminatory and breach Portuguese and EU law," the fund managers, which included Blackrock, said in an email statement.
The names of other financial institutions were not mentioned.
The Bank of Portugal in 2015 had transferred bonds from "good bank" Novo Banco to Banco Espirito Santo (BES) to boost Novo Banco's balance sheet by 1.98 billion euros ($2.11 billion). Novo Banco was created from BES in August 2014 after a 4.9 billion euro rescue.
The bond transfer had caused losses of about 1.5 billion for ordinary retail investors and pensioners and a group representing more than two-thirds of the transferred notes had begun legal proceedings against the Bank of Portugal, the statement said.
Closure of the Novo Banco sale to Lone Star would impair the fund managers clients' claim against Novo Banco and their clients’ ability to recoup losses, the statement said.
Portugal on Friday had agreed to sell a 75 percent stake in state-rescued lender Novo Banco to Lone Star in exchange for a capital injection of 1 billion euros into the institution.
(Reporting by Sangameswaran S in Bengaluru; Editing by Bill Trott)