NEW YORK ( TheStreet) - An asset-management firm speaking for monastic nuns -- and an employee pension plan -- have called for the break-up of Citigroup ( C). Trillium Asset Management, on behalf of the Benedictine Sisters of Mount St. Scholastica, along with the Afscme Employees Pension Plan, are asking the bank to explore a break-up as the stock has consistently traded below book value. The bank's failure to win regulatory approval to return capital earlier this year was also cited as a reason. "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. 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," said Matthew Patsky, CEO of Trillium Asset Management in a statement. "These factors could threaten stockholder return through breakdowns in risk management, increased regulatory scrutiny, higher litigation expense, greater capital requirements and poor public perception, among other challenges." The sisters' web sit describes their mission as including a "thirst for justice and peace that focuses on works of charity as we respond to the root causes of injustice." "There is a gap of almost $50 billion between what Citi says its assets are worth and what the market is saying," said Lee Saunders, Chairman of the AFSCME Employees Pension Plan's Board of Trustees. "It is high time that the board gave shareholders a plan for recovering this value." Other banks including Bank of America ( BAC) and Goldman Sachs ( GS) also trade below tangible book, which has led some analysts, notably CLSA's Mike Mayo, to believe that big banks should consider splitting up. Speculation that Citigroup might consider spinning off more units or accelerate the wind down of its bad bank Citi Holdings has increased since the sudden departure of CEO Vikram Pandit. Newly appointed CEO Mike Corbat, an old Citi veteran, has said that the bank will remain on its current path. However, analysts believe the bank might be able to win regulatory approval more easily under Corbat's leadership. Shares of Citigroup were rising .55% in premarket trading at $36.36. -- Written by Shanthi Bharatwaj in New York.