Public Citizen financial policy advocate Bart Naylor said Capito is "one of the three or four most powerful people in Congress shaping bank law, the law that affects her husband's company."
Naylor added that many conflicts of interest exist among members of Congress.
"For better or for worse, Ms. Capito is not alone," he said.
The letter cites an article published Monday in the Charleston Daily Mail about Charlie Capito's move from United Bank to Wells Fargo Advisors, the investment arm of Wells Fargo & Co.
In March, he took a job managing the company's offices in Charleston, Huntington, Parkersburg and Beckley. He previously worked as a United Bank executive since 2009.
"In [the new] position, Mr. Capito is unlikely to be directly affected by the legislation that you are sponsoring," Public Citizen wrote in its letter.
"At the same time, Wells Fargo claims to be the second largest bank for consumer deposits in the United States and the second largest issuer of debit cards," the group wrote. "Fee income from such sources as swipe fees is the highest as a percent of assets among the largest banks in the United States."
Public Citizen also noted that Capito's biography on her website doesn't mention her husband's occupation or employer.
"The only thing that you learn about her husband is that she has one," Naylor said.
Capito's committee on Wednesday endorsed a package of legislation that would restructure the Consumer Financial Protection Bureau in a way consumer advocates say would severely weaken its powers. It did not vote on the swipe-fee bill, Naylor said.
Reach Alison Knezevich at alis...@wvgazette.com or 304-348-1240.