Updated from 5:54 p.m. ET

A ranking Michigan congressman on Monday asked the

Securities and Exchange Commission

to determine why the

New York Stock Exchange

took two years to turn over documents pertaining to illegal trading on the exchange floor and to probe what NYSE officials knew of the trading.

In a letter to acting SEC Chairwoman Laura Unger, U.S. Rep. John Dingell, a Democrat, asked the agency to complete a report by the end of June on the status of changes the exchange has made to remedy the trading situation.

Dingell said he has new concerns about the issue after reading a

story on

TheStreet.com

about documents regarding the trading that the NYSE only recently turned over to the SEC.

The Wall Street Journal

later ran a story on the same subject. Those documents included handwritten notes from NYSE official Donald Siemer that described meetings exchange officials had about the trading in the early 1990s. The notes included the phrases: "Do not tell the SEC" and "nothing in writing."

"

TheStreet Recommends

The Street.com

and

Wall Street Journal

articles raise at least two troubling questions which need to be answered," Dingell wrote Monday. "Why weren't these documents produced two years ago, and what did NYSE officials know about the unlawful activity and when did they know it?"

Dingell also questioned the SEC about its own actions regarding the illegal trading at the NYSE in the 1990s. He asked the SEC to explain what it did when the NYSE provided the agency with a report in 1993 on the type of floor trading now at issue. "Who at the SEC reviewed that report and did they explicitly or implicitly sign off on it or did they raise red flags?" Dingell wrote.

The NYSE and SEC declined to comment on the letter.

The issue stems from an investigation by the SEC and

U.S. Attorney's Office

in the late 1990s of a type of trading by floor brokers known as "flipping," which involves rapidly buying and selling shares of stock at prices between the quoted sale and purchase prices for the security. The SEC has said the practice is illegal when traders take a share of the profits. In 1998, 10 traders and brokerage officials were arrested and charged with securities law violations for that type of flipping. Many of the traders pleaded guilty and several served prison terms.

Dingell had asked the SEC last April for a report on actions the NYSE had taken to address the situation. At that time, he noted in a letter to then-SEC Chairman Arthur Levitt that it had been about a year since the SEC concluded its investigation of the exchange over the floor trading with a harshly worded settlement.

"The SEC 's order directed the NYSE to comply with several undertakings to implement various significant remedial measures for its floor broker regulatory program and floor-trading operations," Dingell wrote. "Please also advise whether this matter is closed or whether there are any ongoing investigations."

Last month the SEC and the U.S. Attorney's Office in Manhattan began asking new questions about how much senior NYSE officials might have known about or enabled the illegal trading after the exchange turned over the documents. The NYSE said it only recently discovered the documents and gave them to the SEC immediately.

The documents came to light in a separate legal case in which a former floor broker, John D'Alessio, is fighting SEC charges that he violated securities laws by flipping on the NYSE's floor. D'Alessio's lawyer in that case, Dominic Amorosa, has argued that the exchange not only knew of, but also encouraged the trading.

D'Alessio is also suing the exchange, and has made those arguments in that case as well. His suit was dismissed by a federal court judge in Manhattan last year, but D'Alessio is appealing.