The regulator has taken action against 11 firms
Eleven firms have been ordered to stop selling so-called penny shares to older investors, the City watchdog says.
The Financial Services Authority (FSA) said some dealers had been targeting older people with high-pressure sales.
The 11 firms were told to overhaul their business model, and six have since ceased trading.
High-risk penny shares have a low market price, are not traded on the main stock market and are difficult to sell on.
The FSA said that people aged over 50 who already had a few shares - often from privatisations - were being targeted.
In some cases, brokers were paid commission to sell a particular share which was then aggressively marketed to consumers, regardless of whether or not it was suitable for them.
"It is totally unacceptable to have consumers pressurised into buying shares. It is all the more disturbing when the risks of those shares have not been set out clearly," said Lesley Titcomb, of the FSA.
"Quite simply, if firms do not treat their customers fairly, they will not be operating in the market."
The FSA urged investors to challenge a brokers' advice, do their own research into a product, be aware of any risks attached and ask what commission a broker got for arranging a sale.