Martin Tilley of Dentons Pensions believes the proposed capital adequacy ruling for Sipp firms could put larger firms at risk as well as small ones.
The proposals from the Financial Conduct Authority would require Sipp firms to hold a minimum of £20,000 in capital, up from £5,000.
This amount will increase further if the firm holds non-standard assets such as commercial property.
Mr Tilley, who is director of technical services at Dentons, said: "You don't want the FCA's approach to be counterproductive where firms which can't meet their capital adequacy requirement are in jeopardy of a wind-up scheme.
"It's not necessarily smaller firms, larger firms have more assets under management and if a large proportion of these are non-standard assets then these push the capital adequacy up even more."
He said the two types of firms he expected to leave the market would be those run on very tight margins and those where Sipps were not a core part of their business.
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He said Dentons was "relatively relaxed" about the proposed capital adequacy requirements. Around 34 per cent of Dentons' assets are non-standard but Mr Tilley said this was below some firms which hold up to 40 per cent.
Some of this was commercial property, which will increase the firm's capital adequacy costs, but Mr Tilley said it was all UK bricks and mortar rather than overseas properties.
"Commercial property is one of our key areas but it's all UK bricks and mortar with very robust due diligence, it isn't overseas and we very rarely have to get rid of them quickly. The problem is overseas hotels which haven't been built yet for example, the secondary market for that is debatable and the value is questionable and the time scale to get rid of it."
However, he felt the FCA's decision to base the amount on assets under administration was "novel."
"The move was a novel one and has had mixed reviews but you have to do what the regulator says and dance to their tune."
He suggested a suitable alternative would be to continue to base it on expenditure but increase the number of weeks worth of capital from six to 26.