JetBlue Airways has raised checked baggage fees — a potential early signal that carriers are shifting higher jet fuel costs onto customers as crude tops $100 a barrel, the New York Post reports.

Fuel, typically an airline’s largest expense after labor, has spiked fast. U.S. jet fuel prices are now around $4.50 per gallon, up more than 80% since late February.

Rising tensions around the Strait of Hormuz — which handles roughly 20% of global oil flows — are already beginning to hit travelers, as airlines move to offset surging fuel costs.

And one of of the first things to go up is the cost of airline tickets.

$1,900 TO FLY OVERSEAS

Last-minute international fares have jumped to about $1,900, from roughly $830–$1,000 before the latest Middle East tensions. Domestic coast-to-coast fares are up about 16%, even accounting for seasonal demand.

So far, demand has held. United Airlines says recent weeks rank among its strongest ever, but warns sustained high oil could add up to $11 billion in annual costs.

Other carriers, including Southwest Airlines, Delta Air Lines and American Airlines, have not yet followed with fee hikes.

If oil remains elevated, however, JetBlue’s move may be just the beginning — with higher fares and more fees likely ahead.