The Lloyds Action Now campaign group state that chief executive Eric Daniels and then-chairman Sir Victor Blank omitted details about the true financial state of HBOS in a prospectus given to shareholders ahead of a vote on whether the takeover should go ahead.
HBOS had been given a Â£24.5 billion loan by the Bank of England in October 2008, a fact not made public at the time, reports the Guardian.
Jim Rai, head of litigation at Winckworth Sherwood, which is acting for Lloyds Action Now, said: "The Â£25.4bn loan was â¦ deliberately kept secret so that Lloyds TSB shareholders were not put off the proposed acquisition of HBOS."
A spokesman for Lloyds said that it had given "through and appropriate disclosure" of HBOS's use of government support before the takeover.
Earlier this year, the bank predicted it will return to profit in 2010 following a loss of Â£6.3 billion in 2009.
By Gary Cooper