Royal Bank of Scotland is set to join Lloyds banking group in restricting some basic account holders to a limited range of cash machines.
Around 1 million RBS customers would be able to withdraw money only from RBS, NatWest, Tesco or Morrison cash machines.
Though the company has blamed the move on costs, critics point out that it would hurt vulnerable customers - those with poor credit ratings or no fixed address, who would not be able to get a bank account.
Meanwhile, the treasury select committee has called for an explanation from banks planning to restrict which cash machines' basic bank account holders had access to.
Chairman of the committee Andrew Tyrie wrote to RBS and Lloyds and said some of the most vulnerable in society could be affected.
Tyrie wrote, ''We are concerned about the restrictions Lloyds and RBS are placing on basic account holders' access to other banks' cash machines.''
In another development more than 10 British banks had been affected by the decision of a ratings agency, Moody's, to cut ratings.