Aviva has announced it will introduce a new charging tier to its platform, with a lower charge of 0.15% for new customers with more than £400,000.
The change takes effect on all portfolios from 17 February.
The move comes after the leading companies in the sector announced new pricing structures.
Fidelity introduced a platform charge of 0.2% between £250,000 and £1 million, compared to Hargreaves Lansdown's fee of 0.25% between investments of £250,000 and £1 million and 0.1% up to £2 million.
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Phil Ralli, head of platform proposition at Aviva, said: "We've listened to our advisers and changed our pricing in line with their growing demand for more flexibility and simpler terms at the higher end of the market.
"Many customers have larger portfolios as they near retirement age and we want advisers to be able to offer competitive rates in order to attract this wider client base.
"This new pricing structure is a clear demonstration of our intention to deliver simplicity, efficiency and cost effectiveness for all our mid-market customers, regardless of the value of their portfolio. It represents a significant development on our platform."
For Aviva customers in the core level of pension portfolio, who benefit from 0.05% discount for insured funds, the new fee equates to a 0.10% charge.
Barclays Stockbrokers has also got involved with the pricing competition. Recently it announced an annual fund administration fee of 0.35% for investments of up to £250,000 from 1 March, which matches Fidelity's new rate exactly and undercuts Hargreaves' fee of 0.45%.
Holly Mackay, managing director at The Platforum, said it will impact a relatively small number of portfolios, with the average account size across all platforms at £142,000 at quarter 3 2013.
She said: "Where it's more interesting is that it starts to open up a few more options for advisers reviewing clients who have been saving into a packaged product for years, accumulating substantial sums.
"This makes the platform more compelling as a pension vehicle, which is presumably why Aviva has applied the most competitive 0.10% tier to pension pots with more than £400,000. Not revolutionary. Not a price war. But a detail worth considering for some advisers reviewing packaged product solutions for wealthier savers."