In the spring of 2009, investigators for the Senate Commerce Committee began looking into complaints about deceptive billing practices on the Internet.

Before the results of the probe became public in a hearing that fall, four members of Congress reported selling all of their stock in one of about 90 companies under scrutiny, the nation’s largest video game retailer, GameStop.

One of the lawmakers, Sen. Johnny Isakson (R-Ga.), was a member of the committee. The other three were Rep. Michael McCaul (R-Tex.), Rep. Lamar Smith (R-Tex.) and Sen. James Webb (D-Va.).

The Washington Post identified the stock sales as part of an ongoing examination of the intersection of the personal finances and professional roles of lawmakers. Congress forbids administrative officials from trading in companies that appear before them and requires federal judges to recuse themselves from cases involving companies whose stock they own.

Members of Congress, however, have created ethics rules that allow themselves to invest in companies that have interests before their committees.

In an interview, Isakson said the timing of his GameStop trades and the investigation was coincidental. He said he was “not engaged at all” in his stock portfolio, which is handled by a professional manager. He said he had no conflict, because he was unaware of the committee investigation at the time, did not attend the hearing and has no memory of the issue.

“I’m not embarrassed about anything,” Isakson said. “I’ve always believed in total transparency, which is why you’ve got all the information you’ve got.”

Isakson’s investment manager, James C. Hansberger of Morgan Stanley Smith Barney, said the senator had not provided any guidance to him about buying or selling the stock.

“Senator Isakson and I have never discussed the company or the stock, GameStop,” Hansberger said in a written statement released by the senator’s office.

The Senate investigation focused on billing complaints from consumers who alleged that online stores were passing their credit card numbers to shopping clubs they did not realize they had joined.

On May 27, 2009, the committee issued a news release announcing the inquiry, naming the shopping clubs but not GameStop. It received little notice.

At the time, Isakson owned between $50,000 and $100,000 worth of GameStop stock. He had purchased it two months earlier for about $27 a share, according to his financial disclosure form.

On June 18, Isakson sold all of his stock in GameStop for about $23 a share. He sold the stock after holding it for less than three months. The other three stocks that he had bought in March he held for longer periods, an average of eight months.

Smith, who had owned the stock since January 2008, sold off shares worth between $1,000 and $15,000 on May 27. In July and October, Smith also sold off all his shares, worth between $3,000 and $45,000, in two other companies being looked at by the Commerce Committee — Pizza Hut’s parent company and Avis Budget Group.

Smith said the trades posed no conflict, because they were handled by his investment advisers without his input.

“For more than 11 years, my securities have been held in an account managed by Bank of America Merrill Lynch,” he said. “I have no control over stock transactions and have no knowledge of what individual stocks are bought and sold.”

Timothy P. Neary, senior vice president/investments at Merrill Lynch, said “there was no conversation whatsoever” with Smith about those trades.

Trusts for McCaul’s wife and children, which also first bought GameStop in January 2008, sold off their entire holdings, worth between $2,000 and $30,000, on Aug. 25. McCaul’s office said he did not know anything about the investments, because they are part of his wife’s wealth, which he cannot access under a legal agreement with her. His office added that he did not discuss his wife’s investments with her.

Isakson, Smith and McCaul are all members of the Congressional Internet Caucus, which brings 133 lawmakers together with nonprofit groups, trade organizations and firms such as Google and Yahoo that advise the legislators about security, software piracy and the latest technology. GameStop is not an adviser to the caucus.

Webb’s wife, who also had owned GameStop since 2008, sold all of her shares — worth between $1,000 and $15,000 — on Oct. 27. Webb declined to answer questions or comment about the trades, spokesman Will Jenkins said.

One lawmaker kept his GameStop stock during the investigation. Rep. Kenny Marchant (R-Tex.) had bought it beginning in 2006 and, after the investigation, still owned $6,603 of the stock. The company is based in Grapevine, Tex., inside his district.

The committee issued its findings at a Nov. 17 hearing. The investigation reported that as many as 35 million people lost as much as $1.4 billion to more than 90 companies. The consumers did not realize they were joining shopping clubs, which began charging their credit cards up to $12 a month.

The clubs split the money with the online retailers, such as GameStop, which made between $1 million and $10 million, the report said.

In the wake of the report, major credit card companies said they would halt the practice, and then-New York Attorney General Andrew Cuomo announced a consumer protection investigation.

GameStop’s stock price had ranged between $20 to $26 over the course of the Senate investigation; after the New York investigation was announced and following a disappointing holiday season, the price fell to nearly $17, its lowest level since 2006.

Without admitting wrongdoing, 18 clubs and retailers paid millions to settle the New York investigation. The payments included $195,000 from GameStop, $78,750 from Pizza Hut’s parent and $207,000 from Avis Budget Group.

When contacted by The Post, GameStop and Pizza Hut’s parent company did not provide comment, and Avis did not return a call seeking comment.

In addition to his role on the Commerce Committee, Isakson is vice chairman of the Senate Ethics Committee. He recently co-wrote a “Dear Colleague” letter laying out the new reporting procedures senators must follow under the Stock Act, which makes it a crime for lawmakers to use inside information gathered through their duties in trading stocks.

This year, Isakson moved his investments into a blind trust, preventing him from knowing many details about his holdings or giving instructions to trust managers. He called the move “the smartest thing to do.”

Researcher Bobbye Pratt contributed to this article.