TORONTO -- A shareholder advisory firm is recommending shareholders of Chicago-based PrivateBancorp (PVTB.O) vote against a proposed takeover deal by the Canadian Imperial Bank of Commerce (CM.TO).

Institutional Shareholder Services says despite some potential short-term volatility if the CIBC deal is rejected, "the upside potential of a stand-alone strategy appears more compelling."

ISS, which advises institutional investors, says PrivateBancorp's earning power as a stand-alone company appears to be growing due in part to a favourable economic backdrop as well as potential reductions in taxes and regulations.

CIBC raised its friendly takeover offer for PrivateBancorp in March by 20 per cent in a bid to win shareholder approval for the deal. The offer valued the U.S. financial services company at about $6.6 billion.

CIBC said it believes ISS reached the wrong conclusion and noted that the offer has the unanimous support of PrivateBancorp's board as well as Glass Lewis, another shareholder advisory firm.

The increased proposal followed a bid by CIBC last summer that was not voted on by shareholders, but ISS also recommended be rejected.