Pension savers who have acted to protect their lifetime allowance through fixed protection could lose the benefit if they are covered by scheme life insurance.
The lifetime allowance is set to be cut from £1.8m to £1.5m on 6 April. People approaching the current limit have until 5 April to apply for fixed protection from HM Revenue & Customs (HMRC).
The rules mean the member must have no further "relevant benefit accrual".
However, law firms said correspondence with HMRC has revealed pension life insurance set up between 2006 and 2012 will count as benefit accrual - meaning fixed protection would be forfeited.
Association of Member-Directed Pension Schemes chairman Andrew Roberts said it had contacted HMRC about the issue and hoped it would "rectify the rules".
Eversheds urged schemes and advisers to check scheme rules to see if life cover benefits are limited to levels paid out by insurance. It said it was a "common rule" for scheme members.
Sackers also warned hybrid schemes - a mixture of defined benefit (DB) and DC - are affected. However, it added a straight-forward DB lump sum death benefit would not jeopardise fixed protection.
View from the front row
Project Libra unveiled
Including SJP and investment trusts
Spent two years at Sanlam
Will also assess FCA's actions