Washington (CNN) Office of Management and Budget Director Mick Mulvaney sent out travel guidance to Trump administration departments and agencies following the resignation Friday of Health and Human Services Secretary Tom Price.

All travel must be pre-approved by White House Chief of Staff John Kelly whether the aircraft is "government-owned, rented, leased, or charted, except space-available travel and travel to meet mission requirements," Mulvaney said in the memo.

The memo said "every penny we spend comes from the taxpayer" and departments and agencies "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."

"Put another way, just because something is legal doesn't make it right," Mulvaney said.

With few exceptions, "the commercial air system used by millions of Americans every day is appropriate, even for very senior officials," he said.

Read More