Citigroup, American Express, JP Morgan Chase and Putnam Investments were fined $81.25m in total to settle claims that brokers were paid to recommend funds.
Regulators also alleged that the firms steered some customers to costlier funds with high levels of commission.
The firms in question neither denied nor accepted wrongdoing.
'Conflict of interest'
Authorities launched an investigation into the marketing and selling of mutual funds - which are popular with small investors across America - eighteen months ago.
A number of banks have already been fined for a practice known as market-timing, in which institutions make short term trades to the detriment of long term investors.
On Wednesday, the Securities and Exchange Commission (SEC) handed out civil fines worth $20m and $40m respectively to Citigroup, the world's largest financial services company and Putnam Investments, a subsidiary of Marsh & McLennan.
In a connected move, the National Association of Securities Dealers said Citigroup, American Express and JP Morgan Chase had agreed to pay $21.25m in total for alleged violations in the sale of mutual funds.
| Industry professionals must fully inform
their customers of the nature and extent of any conflicts of interest that
may affect their recommendations Securities and Exchange Commission |
Incentive allegations
The SEC said Citigroup failed to tell customers buying mutual funds through its Smith Barney retail unit that it only marketed funds which offered incentive payments in return for being promoted.
The watchdog also alleged that Citigroup recommended and sold funds offering a lower level of return to investors because they delivered higher levels of sales commission.
"We hope securities industry professionals have by now received the message that they must fully inform their customers of the nature and extent of any conflicts of interest that may affect their recommendations," said Stephen Cutler, SEC's enforcement director.
Putnam Investments said the firm had terminated the practices which were the subject of the investigation over a year ago.
Citigroup and American Express said they were pleased to settle the regulatory issues and stressed they had amended their sales practices.