NEW YORK (CNN/Money) - The National Association of Securities Dealers has suspended and fined six current or former Credit Suisse First Boston executives for their roles in steering hot initial public offerings to customers willing to pay tens of millions of dollars of improperly high commissions.

The association, which runs the Nasdaq exchange, fined J. Anthony Ehinger, CSFB's global head of equity sales, and George W. Coleman, its institutional listed sales trading head, $200,000 each, and suspended them for 30 days in all capacities, and another 30 days as supervisors.

In addition, former CSFB employees Scott Brown, Richard Scott Bushley, Michael Grunwald and John Schmidt were each fined $30,000, and suspended for one year each, for failing to provide NASD with timely testimony in its probe.

All six executives have signed agreements accepting their suspensions and fines without admitting to their guilt.

CSFB already was hit with censure in January and agreed to pay $100 million in fines, split evenly between NASD and the Securities and Exchange Commission, for its role in the IPO scandal.

"CSFB resolved all outstanding investigations of the firm by the NASD and the SEC with respect to these matters and had taken internal disciplinary action against the employees involved," said a statement from the firm Thursday. "At that time, CSFB understood that regulators were continuing their investigations of the individuals."

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CSFB had already fined Ehinger and Coleman $500,000 each in February, as well as a number of other executives not named Thursday by Nasdaq between $250,000 and $500,000, according to a source familiar with the matter.

During the period the NASD says improper activities took place, from April 1999 to June 2000, hot IPOs, especially for tech companies, often more than doubled in value from the offering price in the first day's trading. The investment banks that handled the offerings, like CSFB, were able to put favored customers into the IPOs at offering prices, virtually guaranteeing them a substantial profit.

The NASD charges that customers, especially institutional shareholders, who were being given a chance to buy into IPOs at the offering price were being charged commissions of up to a third of their profits, which NASD charges equaled tens of millions of dollars in excess commission compared with CSFB policy. Since CSFB staff compensation was based on commission payments by their clients, the individuals named in Thursday's action benefited from the improper arrangement, NASD charges.

Last month NASD proposed new rules regarding allocation of hot IPOs to control future abuse, but a cooling of the IPO market has also significantly reduced the opportunity for such schemes to work.