A high-ranking Obama administration official unlawfully billed taxpayers more than $4,000 for taxi rides from his home to the U.S. Patent and Trademark Office headquarters, an internal investigation has found.

Vikrum Aiyer, who served as chief of staff of the agency, a part of the U.S. Department of Commerce, forced taxpayers to foot a bill for at least 130 unauthorized taxi rides – the majority of which occurred during a four-month period in 2016, according to a report released Tuesday by investigators, the Washington Post reported.

Aiyer previously served as President Obama’s senior policy adviser at the National Economic Council. He allegedly impersonated other current and former high-ranking agency officials, using their names on taxi receipts to avoid being caught in the unauthorized scheme.

But the ruse was soon discovered after officials started raising questions. They confronted the Patent and Trademark Office’s then-communications director – one of the names Aiyer used to bill the rides – who told investigators that he did not use the taxis as he regularly drove to work.

“The evidence … establishes that Political Appointee knowingly used the Agency’s Cab Company account for impermissible purposes on a routine basis and that he took steps to conceal his unauthorized use of this account by providing false names and false location information,” Commerce Department Investigator General Peggy Gustafson wrote in the report, according to the Post.

Aiyer’s use of government money to pay for his commute violated federal policy prohibiting such practices.

He did not deny the findings during an interview with investigators in December 2016. Instead, he justified the practice by saying other officials allegedly did the same.

“Political Appointee said he thought it was permissible to provide incorrect trip origin or destination information because this was the ‘protocol that was imparted to [him] by [his] bosses at the time,’ and ‘because this is how … prior bosses approach[ed] it,’ ” investigators wrote, according to the Post.

Over two years, the government paid Alexandria Yellow Cab, a company contracted to provide authorized cab services to agency’s officials, well over $4,000 for Aiyer’s rides, the report said.

While most of the cab rides took him to and from work, investigators also found that Aiyer sometimes used the agency’s cab account to “facilitate his weekend social activity ... but he made it appear otherwise when arranging for these cabs.”