Pension schemes are able to charge to implement a pension sharing order.
There is no maximum set by legislation, but the National Association of Pension Funds (NAPF) has issued guidance to its membership which sets out a range of charges.
Below is a link to the NAPF guidance.
I would suggest that if a scheme is charging more than the guidance then it may be appropriate questioning this with the scheme trustees.
It is important to note that if the schedule of charges is not provided at outset then it is possible that charges cannot be levied. Also once the schedule of charges has been provided the level of charges can only be increased in line with inflation.