A "significant number" of firms mis-sold financial products by banks have been "treated unfairly" by a compensation scheme, MPs have reported.
The scheme was set up to compensate firms mis-sold interest rate hedging products.
The Treasury Committee has urged the Financial Conduct Authority (FCA) to demonstrate that the scheme has not "unduly favoured the banks".
MPs said the review should be overseen by an independent party.
"It is far from clear that the FCA's scheme has delivered fair and reasonable redress to all the businesses affected," said Committee chairman Andrew Tyrie.
"The FCA needs to do much more to demonstrate that this process is credible and has not unduly favoured the banks."
The MPs also called on the FCA to explain why it had introduced a £10m cap on the value of the interest rate hedging products considered eligible for inclusion in the scheme.
It said this decision meant a third of firms were excluded from participating, and questioned whether this was "a concession to bank lobbying".
The mis-selling arose when banks insisted that small firms applying for loans had to take out insurance against a rise in interest rates, often making repayments unmanageable.
That insurance took the shape of so-called "swap" contracts, also known as interest rate hedging products, which would usually pay out if rates rose by more than one or two percentage points.
What the bankers did not tell the businesses was that the "swap" contracts also worked in reverse. If interest rates fell, it would be the business, not the bank, that paid out potentially huge sums.
In other words, the businesses were effectively insuring the bank against interest rate falls.
When rates hit rock bottom in March 2009, instead of benefiting from cheaper repayments, the businesses found themselves coughing up hundreds or thousands of pounds extra in premiums for the swap contracts.
If they wanted to get out of them, the exit cost commonly ran into hundreds of thousands of pounds.
In 2013, the then regulator - the Financial Services Authority (FSA), now the FCA - found that more than 90% of these swap contracts had been mis-sold.
It subsequently agreed the terms of a compensation scheme with nine banks, including Royal Bank of Scotland, Lloyds Banking Group, Barclays and HSBC.
But Mr Tyrie said: "A significant number of those firms who were mis-sold these hedging products feel that, having been ripped off in the first place, they have now been treated unfairly again."