A firm that advises one of the largest public unions in the U.S. requested on Wednesday that Citigroup mull the possibility of breaking up its financial supermarket, putting new public pressure on the beleaguered banking giant as it undergoes a leadership transition.

Trillium Asset Management, a shareholder advisory firm with more than $1 billion in assets under management, effectively renewed call made recently by Sandy Weill, Citigroup’s former CEO and one of the founding fathers of the “financial supermarket” concept that helped turn Citi into a global banking behemoth.

Citing a languishing stock price and concerns about the bank’s long-term solvency, Trillium — representing the pension arm of the American Federation of State, County and Municipal Employees — said in a statement that Citi should “a possible separation of one or more of its business units.”

"Despite some positive steps taken since the start of the financial crisis, we believe Citigroup's progress toward simplifying and de-risking its business has been slow and incomplete,” said Matthew Patsky, CEO of Trillium Asset Management, in a statement.

“Citigroup boasts many attractive attributes, but remains burdened by excessive complexity, as well as the stigma and risks associated with being named a 'too big to fail' institution,” he added. The firm did not cite how many shares of Citi’s stock it owned.

After forging the concept of the modern super-bank in the 1990s, Citigroup has fallen on tough times. The bank was laid low by the 2008 financial meltdown, being forced to subsist on a whopping $476.2 billion in total bailout money — more than any other Wall Street bank.

The banking giant is under increasing pressure following the surprise departure of former CEO Vikram Pandit, who steered Citi through the rough shoals of the financial crisis. In a completely unexpected move last month, Pandit departed Citi’s executive suite and handed the reins over to Michael Corbat, an investment banking veteran.