Rules around the tapered annual allowance could lead to people breaching their tax relief limits if they don't use an adviser, Prudential has warned.
The provider said the new rules, which affect people with threshold income of more than £110,000 and "adjusted income" of more than £150,000, are so complex that consumers might find them difficult to follow.
Vince Smith-Hughes, director of specialist business support at Prudential, said the rules could start affecting higher earners in 2018 who had previously been able to maintain their pension contributions through the use of carry forward.
"This won't last forever, and there is a danger that some unadvised individuals will maintain their existing pension contributions without realising they are breaking a much lower allowance limit," he said.
The annual allowance and tapered annual allowance were the most popular subjects on Prudential's adviser helpline in 2017, attracting 1,594 calls.
The annual allowance is the limit to the total amount of contributions that a saver can pay into their defined contribution pension and claim tax relief on and is currently capped at £40,000.
Amounts exceeding the limit will be taxed at the saver's marginal rate of income tax.
But in April last year the government put in place a tapered annual allowance for savers earning more than £150,000.
This means there is a reduction in the annual allowance of £1 for every £2 that the adjusted income exceeds £150,000, up to a maximum reduction of £30,000.
Mr Smith-Hughes said: "Given the complexity of the rules it is almost impossible to believe many of those not receiving advice will be able to navigate their way to establishing what they can pay into a pension without incurring an annual allowance charge.
"Much angst is likely to follow when the unexpected tax bills arrive."
Investment firm Hargreaves Lansdown agreed January could be a divisive date.
Nathan Long, senior pension analyst at Hargreaves Lansdown, said: "The deadline for filing tax returns in January could see a deluge of enquiries from people who have inadvertently overpaid.
"The ability to carry forward unused contributions from previous years will save some, but not all of these people from a tax penalty."
carmen.reichman@ft.com
