Federal Election Commission records analyzed by the Blotter on ABCNews.com show Thompson's committee paid $178,000 to his son's political consulting firm, Daniel Thompson Associates, since 2003.
In contrast, the committee made only $66,700 in contributions to other campaigns and political committees in the four years since Thompson retired from the Senate.
The payments to Thompson's son were described as for management and consulting services.
While it is not unusual for members of Congress to hire family members to work on their campaigns, the high payments to Thompson's son's consulting business deserve close scrutiny, according to Sheila Krumholz, executive director of the Center for Responsive Politics.
"It raises eyebrows and calls into question whether this is self-dealing," says Krumholz .
Contacted at his Nashville, Tenn., political consulting business, Daniel Thompson told ABC News he couldn't talk because he was "about to leave for a business trip" and referred all questions to a spokesman for his father, who did not return calls from ABC News.
When Thompson left the Senate in 2002, he converted more than $370,000 in leftover campaign funds into a "leadership PAC," which allowed him to contribute to other politicians at a $5,000 limit and pay for a variety of other expenses, including travel and consulting services.
Krumholz says retired lawmakers, like Thompson, often keep leadership PACs as a "slush fund" to help them set the stage for a run for higher office.
"Often it is simply a way to keep their foot in the door and keep them in the spotlight," says Krumholz.