In an announcement made earlier this month, the US Postal Service told customers that as of May 16, they will no longer ship electronics like iPads, Kindles, smartphones and other devices containing lithium batteries overseas.

This means that people who want to ship electronics to troops serving abroad will have to pay a premium to go through private shipping services.

After working on an agreement with two unions that issue semi-binding regulations for global trade, the post office has determined that it can no longer ship items with lithium batteries overseas. The unions do not allow lithium batteries in mail shipments on international commercial flights, while they do allow them in non-mail shipments, like private courier services.

There is a risk of explosion from improperly installed lithium batteries, so, in an effort to protect pilots and other shipping employees, the trade unions do not want the batteries shipped across oceans on commercial air transportation. This means that families attempting to ship iPads, Kindles and laptops to their loved ones serving overseas will have to pay a premium to get them there through a private courier.

Companies like Apple and Amazon that ship these products to consumers in large quantities ship them with a minimal charge, which greatly reduces the risk of explosion. When private citizens ship them, there is no way to know if the batteries have been fully charged, improperly stored or improperly packed. Lithium batteries have been blamed for at least two fatal cargo plane crashes since 2006.

[Fast Company]