Amazon is deepening its push into logistics, in a massive challenge to incumbent parcel carriers.

FedEx and UPS shares fell after Amazon announced it was allowing other businesses to use its extensive supply chain network to move and store goods.

It’s “a shot across the bow to the entire transport market,” one analyst said; another called it a “watershed moment” for North American freight. Truckers, railroads, and warehouse operators could all take a hit.

The freight industry is already grappling with turmoil stemming from the Iran war. FedEx and UPS have both raised fuel fees as energy supply disruptions make ground and air commerce more expensive.