Amy Newson claims she was told to take out a NatWest personal pension instead, because her monthly contributions into the occupational scheme were higher than she could afford.
The advice she received followed months of letters from the bank in which it repeatedly pressed her over the repayment of an overdraft incurred when Miss Newson, now aged 24, was a trainee teacher.
She said: 'I believe they were using my debt with the bank as a lever to sell me a personal pension. To then persuade me to use my existing contributions to help pay off my overdraft is immoral.
'If they wanted me to repay what I owed they should have made their demands without reference to my pension. I have lost 18 months of contributions as a result.'
Miss Newson's battle with her bank began shortly after she completed her training course in June 1992 and began working as a teacher at Camden School for Girls, in north London, that autumn.
Her overdraft of a few hundred pounds grew to pounds 1,700 when she paid a month's deposit and rent in advance on her new flat. It was still at that level in February 1993, when she met her branch's assistant manager and a financial adviser to discuss taking out a loan to repay the debt.
She said: 'They asked me to produce my pay slip, as they claimed they needed this to complete the loan application form. On production of the pay slip, they commented on the size of the superannuation contribution, which they said seemed rather a lot for my age.
'I told them that I only intended to stay in teaching for about 10 years. They informed me that my contributions were wasted.'
Miss Newson claimed she was also told that she could ask for a refund on her existing contributions, to which she was entitled because she had worked as a teacher for less than two years. The money, about pounds 450, could then be used to offset the size of her loan.
She agreed to do this. In July 1993, she also began paying pounds 30 a month into a personal pension with NatWest. The bank has since been in touch with her, suggesting that contribution should rise to pounds 70 a month.
'At Christmas, I went home and spoke to my mother about what I had done. She trained as a financial consultant and was horrified by what had happened. After all the publicity about pensions in recent weeks, I am worried. I don't believe I was given proper financial advice.'
National Westminster said: 'We are investigating this complaint and take the matter very seriously.
'If we find that poor advice was given, or that the customer was pressured by financial circumstances into following bad advice, then we shall fully rectify the position.'