(CNN) As Democrats in Congress seek to conduct oversight and request more information from the federal agencies, they are running into an odd roadblock at the Interior Department where the acting secretary says he can't provide his calendar to lawmakers because he doesn't have one.

In response to questions about the transparency of his government schedule, acting Interior Secretary David Bernhardt said he does not personally maintain a calendar and has no legal obligation to do so.

Bernhardt, a former oil and gas lobbyist whom President Donald Trump formally nominated Friday to permanently lead Interior, sent a letter, shared with CNN by an environmental group, in reply to a request from Democratic lawmakers for records providing more detail on his meetings.

Rep. Raúl Grijalva, who chairs the House Natural Resources Committee, stated in a February 7 letter that more than 100 hours of official government time on Bernhardt's schedule did not include descriptions of his meetings or list the non-Interior attendees. The letter asked Bernhardt for all copies of all his calendars and schedules.

Bernhardt replied last week that while no agency guidance specifically recommends he keep a calendar, others create schedule entries for him to organize his daily appointments, which he said are carefully screened by ethics officials when they involve nongovernmental parties.

"I have not personally maintained a calendar for years, and I have no intention of suddenly doing so now," Bernhardt wrote.

He added that he consistently follows the guidance of ethics officials, and that shortly after becoming Interior's acting secretary, he committed to publishing all of his nongovernmental meetings on Interior's website, and he challenged Grijalva to do the same.

"I encourage you in your new leadership role to join me in adopting this disclosure procedure. Together, our leadership on this issue will provide a good example," Bernhardt wrote.

Bernhardt's response comes as senior Democratic lawmakers with sprawling demands for documents have accused the Trump administration of an unprecedented level of stonewalling, a notion strongly disputed by the White House and the federal agencies who say they are working in good faith.

Bernhardt said in his letter Interior would work to make necessary records available to the House committee staff. When asked why Interior had not yet publicly released copies of Bernhardt's schedule since September 2018, Interior spokesperson Faith Vander Voort said the department's records office has a backlog of requests.

Interior's website has included summaries of Bernhardt's daily appointments since he became acting secretary in January, but many of the entries have descriptions such as "External Event/Intergovernmental" or "Staff Meeting" without further detail.

Some postings do include descriptions of meetings with nongovernmental attendees. For example, an entry for one week in February shows he met with the United Services Automobile Association, also known as USAA, and the Rocky Mountain Elk Foundation, a conservation and hunting organization.

Grijalva's letter stated some of Bernhardt's previously released calendars did not disclose that certain meetings included lobbyists such as Brian Ballard, who previously lobbied for the Trump Organization. The letter states the omission "raises questions about the intent to hide or manipulate federal records to avoid disclosure."

A spokesperson for Grijalva did not respond to a request for comment.

Bernhardt's calendars have not disclosed other interactions with energy-industry representatives, according to a CNN review of some Interior documents.

For example, a calendar entry for September 22, 2017 shows Bernhardt attended a "Meeting to Discuss Energy Issues" with no listed attendees. But Interior visitor logs show that minutes before that scheduled meeting Bernhardt signed in Jack Gerard, the then-CEO of the American Petroleum Institute, an association whose members include some of Bernhardt's former clients, according to Interior documents first identified by the watchdog organization Documented.

An API spokesperson did not share details about the interaction with CNN but said the organization regularly engages with officials at all levels of government.

Aaron Weiss, deputy director of the Center for Western Priorities, a conservation group that has been critical of the Trump administration, said he did not understand why Bernhardt did not share all copies of his internal schedule maintained by his staffers with the House committee.

"These are not complicated records. You can print out your Outlook or Google calendar right now," said Weiss, who shared the letter with CNN. "So either the Bernhardt calendars don't exist, or they're hiding something that would put his nomination at risk."

Weiss said that Interior has not publicly released actual copies of Bernhardt's internal schedule for months, even though his letter states that the details of the schedule he receives each day are publicly provided.

CNN previously reported that some meetings were kept off the public calendar of Ryan Zinke, who resigned as Interior secretary in December amid multiple ethics investigations. Some of those meetings involved business representatives, and other meetings were so vaguely described that the public could not tell what he was doing or with whom he was meeting.

Bernhardt has faced additional questions regarding his interactions with the energy industry.

CNN reported that since Bernhardt joined Interior in 2017, the agency has made at least 15 policy changes, decisions or proposals that would directly benefit Bernhardt's former clients, and that in each case, the past clients shared comments or requests that the department's actions have granted or aligned with.

Democratic Sens. Elizabeth Warren of Massachusetts and Richard Blumenthal of Connecticut asked Interior's inspector general to investigate Bernhardt's actions after The New York Times reported he has worked to strip away rules also opposed by his former client Westlands Water District related to the delta smelt, a California fish.

Vander Voort said Bernhardt has fully complied with his recusal agreements and that any critics who suggest he has crossed ethical lines with his former clients are either incorrect or deliberately misleading.