Commerce Secretary Wilbur Ross takes his seat to testify before a Senate Finance hearing on "Current and Proposed Tariff Actions Administered by the Department of Commerce" on Capitol Hill in Washington, U.S., June 20, 2018.

Lawmakers will grill Commerce Secretary Wilbur Ross in March about a "wide range" of topics, including Ross' role in the Trump administration's plans to add a citizenship question to the 2020 census.

Ross agreed to testify "voluntarily and without a subpoena" after weeks of discussions, House Oversight Chairman Elijah Cummings, D-Md., said in a statement Tuesday. A spokesman for Cummings confirmed to CNBC that the hearing will be public.

"Committee Members expect Secretary Ross to provide complete and truthful answers to a wide range of questions, including questions regarding the ongoing preparations for the census, the addition of a citizenship question, and other topics," Cummings said in the statement.

He also noted that the majority-Democrat committee expects Ross, who has served in President Donald Trump's Cabinet since the early days of his administration, to comply with multiple outstanding requests for documents that have been "withheld" by the Commerce Department.

The Commerce Department did not immediately respond to CNBC's request for comment on Cummings' letter. But a spokesperson told NBC News that the department "is working with Chairman Cummings and Ranking Member Jordan to determine a mutually-agreeable date for the Secretary to appear before the Committee."

The hearing, which Cummings' statement says is set for Thursday, March 14, comes a week after a federal court in New York blocked the Trump administration's plans to include a question in the 10-year national survey asking respondents about their citizenship. The Trump administration is appealing that ruling.

Ross, whose department oversees the census, had argued that the question was necessary in order to uphold certain provisions of the Voting Rights Act.

The Cabinet secretary "cherry-picked" evidence, "acted irrationally" and failed to justify the planned policy shift, U.S. District Court Judge Jesse Furman wrote in his conclusion. Furman added that the plaintiffs did not meet their burden of proof in claiming that Ross' decision was "motivated by invidious discrimination."

The results of the census are used to distribute congressional district seats, a process that is fiercely contested and scrutinized by watchdogs, advocacy groups and political parties. Civil rights groups have argued that the proposed citizenship question — "Is this person a citizen of the United States?" — could create a chilling effect that would result in a lower count of minority respondents, especially Latinos.

The question has appeared in various forms on past censuses. But it has not appeared on the "complete" survey since 1950, The Washington Post reported, though it has been included on other forms in subsequent years.

Some Democrats in Congress have also questioned Ross' prior testimony before the Ways and Means Committee — in particular his assertion that the Justice Department "initiated" the citizenship question request.

Ross has also been accused by a campaign-finance watchdog of possibly violating criminal conflict-of-interest laws by holding stock in companies potentially affected by Trump administration actions in which he was involved.

The Campaign Legal Center flagged Ross' role in a Trump administration investigation on whether to impose steel tariffs while Ross held stock in his former investment management firm, which has a "major interest" in Chinese steel. The center also questioned why Ross did not initially disclose his stake in another steel-based manufacturer, Greenbriar, and shipping company Navigator.

The watchdog asked the Commerce Department's inspector general's office to conduct an investigation.