(Bloomberg) -- Mayor-elect Bill de Blasio’s plan to pump $1 billion of New York’s $144 billion in pension assets into apartments for poor and working-class residents faces constraints including competition from banks and declining federal aid.

Trustees of New York’s five retirement plans have a fiduciary responsibility to maximize returns for beneficiaries. That means they can’t provide below-market financing to help de Blasio achieve his goal of creating or preserving 200,000 affordable units in 10 years, said advocates such as Moses Gates of the Association for Neighborhood and Housing Development.

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