U.S. Trade Representative Robert Lighthizer speaks during a meeting on trade held by U.S. President Donald Trump with governors and members of Congress at the White House on April 12, 2018 in Washington, DC.

President Donald Trump's trade representative spent more than $900,000 furnishing two Washington buildings — but says it was just following a plan set in motion under President Obama.

The Office of U.S.Trade Representative Robert Lighthizer, or USTR, spent $912,278.48 on "furniture and workspace changes" in its two offices under the Trump administration, a source familiar with the expenditures told CNBC.

The expenditures were part of a long-planned project that began during the Obama administration, said Assistant U.S. Trade Representative Fred Ames.

In a statement to CNBC, he said the investment plan began before 2014 and was intended to "install wall systems in work spaces and replace two-decade-old office furniture in two buildings to achieve improved functionality and gain much-needed additional office space."

"Ambassador Lighthizer did not direct these expenditures, which were planned and executed consistent with career staff's spending authority," Ames said. "In my opinion as a senior career official responsible for developing and implementing this project, these funds were critical for continuing to execute effectively USTR's mission."

The New York Post first reported the expenditures on Tuesday. Citing contracts it reviewed, the Post reported that, among other expenses, the USTR spent $290,000 on movable wooden wall systems, and paid $475,000 to furniture-maker Executive Furniture of Washington, DC.

The furniture company declined to comment on the sale to CNBC, claiming the information was confidential.

The Post reported that prior trade representatives under the Obama administration spent much less on furniture during a comparable time in office. Lighthizer's predecessor, Michael Froman, spent $151,000 on office furniture during a similar time span, according to records reviewed by the Post. Obama's first trade representative, Ron Kirk, spent $237,000 during his first 15 months in office, the Post reported.

In an interview with CNBC, Kirk said he was "almost 100 percent sure" his office wouldn't have approved such an investment plan by the time of his departure because his office was deeply affected by the government sequester raging in Washington at the time.

Kirk added: "At least in terms of my executive office, I didn't spend a dime."

Kirk's tenure ended in March 2013; he was succeeded by Froman, who was confirmed to the office in June that year. Froman, who was hired by Mastercard in April, did not respond to CNBC's requests for comment.

A source familiar with the expenditures told CNBC that Lighthizer's executive office received none of the more than $900,000 spent on furniture, nor did he direct the expenditures. Rather, three separate invoices totaling $5,189 went toward the ambassador's office, which fell within his authorized allowance.

A former Obama trade aide told the Post that it was "laughable" to suggest the Trump administration was merely following an Obama-era plan, when Trump had already made seismic changes to Obama's policies. The aide cited Trump's early withdrawal from the Trans-Pacific Partnership trade pact in order to argue that "furniture purchases cannot be as binding as a trade agreement."