Most air travel by federal officials on government and chartered aircraft will now be subject to approval by White House chief of staff John Kelly, according to a memo the Office of Management and Budget (OMB) circulated to agency heads on Friday.

The memo comes as Health and Human Services Secretary Tom Price announced his resignation Friday, amid concern over his extensive use of taxpayer-funded private charter planes and military jets for domestic and foreign business travel. In the memo from OMB Director Mick Mulvaney to agency and department heads -- a letter prompted by a request from President Trump -- Mulvaney outlined the new process for air travel requests. Most requests will have to receive prior approval from Kelly, while OMB reviews "longstanding guidance" to determine how to improve existing controls, Mulvaney wrote.

Mulvaney's memo said commercial air travel that millions of Americans use every day, with very few exceptions, "is appropriate, even for very senior officials."

"Therefore, all travel on government-owned, rented, leased or chartered aircraft, except space-available travel and travel to meet mission requirements ... shall require prior approval from the White House chief of staff," the letter says. "Full-time required use travelers are exempted from this requirement. Further guidance from the White House chief of staff on the approval process will be forthcoming. OMB is also reviewing longstanding guidance pertaining to the use of government-owned, rented, leased, and chartered aircraft and welcomes any suggestions that would strengthen existing controls."

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Mulvaney's memo did remind agency heads that government-owned, rented, leased or chartered planes shouldn't be used without "specific justification," but also said public servants should consider more than just federal travel regulations.

"Every penny we spend comes from the taxpayer," the memo says. We thus owe it to the taxpayer to work as hard managing that money wisely as the taxpayer must do to earn it in the first place."

Price isn't the only secretary under scrutiny for his travel. Treasury Secretary Steve Mnuchin's travel is under review by the Treasury Department inspector general after he reportedly used a government plane to view the eclipse, and Environmental Protection Agency head Scott Pruitt spent at least $58,000 on non-commercial travel, CBS News has reported.

Here is the full text of the Friday memo: