Low-cost airlines, estate agents and gyms are among businesses which face being taken to court over hidden charges under proposals put forward by legal reform bodies.
Courts should have the power to scrutinise the fairness of costs tucked away in small print, the Law Commission and the Scottish Law Commission say.
Under current laws, courts have the power to assess the fairness of a contract, but are unable to look at the price.
The commissions recommend courts should not interfere with prices which are "transparent and prominent". But when charges are hidden in small print, they should be given the power to assess them for fairness.
They add that small print is not "just about font size" – it also includes poor layout, densely phrased paragraphs and legal jargon.
The rise of price comparison websites has piled pressure on traders to advertise low headline prices, while earning profits through other charges, the commissions say.
David Hertzell, the Law Commissioner leading on the project for England and Wales, says: "The current law is baffling – so much so that consumers and regulators are reluctant to challenge unfair charges.
"Both traders and consumers need clearer law. If a price is transparent and prominent, the courts should not interfere – but other charges need to be fair."