MEAFs are the latest financial product to come under scrutiny, following concerns over credit card payment charges and payment protection.
The FSA announced last September that it would be looking into the issue of MEAFs and whether or not consumers were being unfairly treated.
An existing clause in mortgage contracts allows the lender to change the fee, providing it can provide a valid reason.
The FSA said in a statement: “After examining a number of mortgage contracts, the FSA considered that some were not as clear as they could be in explaining which costs would be charged to the consumer at what time or event in the life of the contract.
“The FSA has asked some lenders to consider whether their terms might be unfair, and to provide it with evidence of how decisions to increase their MEAFs were taken.”