Some Senate Democrats want the Department of Commerce's internal watchdog to investigate whether Ross was not fully forthcoming during his confirmation process earlier this year and whether he has fulfilled promises to resolve potential conflicts of interest. The lawmakers are also asking the agency's inspector general to examine Ross's chief of staff, Wendy Teramoto, over possible conflicts.

The call for an investigation comes shortly after a series of reports questioning Ross's investments. A group of investigative journalists unearthed information connecting one of Ross's shipping assets, a company called Navigator, to a Kremlin-linked company. The revelations surfaced as a result of the so-called Paradise Papers, leaked documents that exposed how wealthy people, governments and corporations have avoided taxes and scrutiny by using offshore companies.

A spokesperson for the Commerce Department said Ross wasn't involved with Navigator's decision to "engage in business" with the Russian company.

The secretary works closely with the agency's "ethics officials to ensure the highest ethical standards, and is committed to restoring our economy and creating American jobs," said the spokesperson in a statement to CNN.

The Democratic congressmen say they asked Ross about offshore accounts in a written questionnaire before his confirmation hearing. They now claim Ross misled them.

"Secretary Ross's written responses to these questions only revealed some stock and a board membership in Arcelor Mittal and a bank account in Ireland with the equivalent of about $58,000," the six lawmakers -- Sens. Richard Blumenthal of Connecticut, Maggie Hassan of New Hampshire, Cory Booker of New Jersey, Maria Cantwell of Washington, Tammy Baldwin of Wisconsin and Tammy Duckworth of Illinois -- wrote in a letter to Peggy Gustafson, the agency's inspector general.

Although Ross didn't mention any Cayman Islands entities in response to the questionnaire, he did list those companies on his financial disclosure form.

Shortly after the release of the Paradise Papers, Forbes magazine accused Ross of inflating his net worth by billions of dollars. The publication asked why Ross's government financial disclosure form suggested he was worth at least $2 billion less than Forbes had reported last year in its annual list of the 400 richest people in America.

Like other administration appointees, Ross underwent the government's vetting process before he was confirmed, which required him to report his assets. In his ethics agreement, also part of the process, he pledged to sell 80 assets to resolve any potential areas of conflict.

Democrats praised him at the time for his transparency and making the "personal sacrifice" to divest millions in assets.

"Let me focus on another area where I think you have really made a very personal sacrifice," Blumenthal said during Ross's January confirmation hearing. "Your service has resulted in your divesting yourself of literally hundreds of millions of dollars in assets so that you can reach an agreement with the Office of Government Ethics. ... You have resigned from 15 positions. The process has been enormously complex and challenging and costly to you personally, correct?"

"Yes sir," Ross responded at the time.

Florida Democratic Sen. Bill Nelson praised Ross for "placing the public's interest ahead" of his own, adding that he hoped President Donald Trump would follow Ross's lead and eliminate "any business dealings that could pose potential conflicts of interest."

The lawmakers, who were consumed at the time by Trump's potential conflicts of interest, didn't challenge Ross on the assets he got to keep.

Government ethics officials allowed Ross to retain ownership of companies in two industries: transoceanic shipping and real estate financing. In exchange, Ross signed an ethics agreement that calls for his recusal in "any particular matters affecting the interests of these entities and their holdings." The document also suggests that Ross shouldn't participate in decisions affecting those two industries.

Now the Senate Democrats want the agency to investigate whether he's recusing himself appropriately. By doing so, they are casting doubt on his commitments and whether his policy recommendations could "further aid his business interests."

"The Secretary recuses himself from matters focused on transoceanic shipping vessels, but has been supportive of the Administration's sanctions against Russian and other entities," the Commerce statement said.

The Democrats are also asking commerce to confirm that Ross has made good on his promise of divesting assets. The Office of Government Ethics website, for example, is missing reports that would confirm the sales of 14 of the 40 assets Ross promised to divest within 90 days of his confirmation. Ethics experts say there could be legitimate reasons Ross didn't file those reports. For example, he wouldn't be required to file them if he had given away the assets instead of selling them.

The Democratic lawmakers also are asking the agency to investigate Ross's chief of staff. They cite unnamed news reports that Teramoto was a board member of Navigator -- the shipping company in which Ross owns a stake -- until July 17. She had begun working at the Commerce Department months earlier, according to those same reports.

"These reports about a clear and compelling conflict of interest make us question whether her efforts are focused on her personal business interests or the well being of the American people," wrote the lawmakers.