"In the absence of any real movement here it must be now up to government to correct this anomaly created through unintentional legislation and ensure that the impacted many receive what is rightfully theirs."
Other master trusts are aware of this problem, with Smart Pension pledging last year to introduce a relief at source option during this year.
Martin Freeman, head of Smart Pension's product development division, said: "We're making sure we get it right because it is easy to trip up with relief at source and mistakes can be costly.
"We support the call to help people who most need it and we are building the robust automation that is necessary for relief at source."
Now: Pensions announced in September that it would be topping up pension pots of non-taxpayer members to make up for the income tax relief shortfall, which was extended until April.