Rules for fixation of pay of re-employed civilian pensioners with public sector banks?

I am a retired Group 'A' Gazetted Officer from Central Govt and re-employed with a nationalized bank.There are some rules under which last pay drawn at the time of retirement is protected when a Group 'A' pensioners are re-employed in Government service or service with public sector undertaking like nationalized banks.but my bank refused to protect my last pay drawn.