By Lisa Baertlein

A threatened U.S. strike at United Parcel Service could be "one of the costliest in at least a century," a think tank specializing in the economic impact of labor actions said on Thursday.

Potential losses from a 10-day strike at the world's biggest package delivery company could top $7 billion, according to an estimate from Michigan-based Anderson Economic Group. That number includes UPS customer losses of $4 billion.

A UPS work stoppage could delay millions of shipments ranging from e-commerce packages to electronic components and lifesaving prescription drugs, experts warned.

Talks between the company and the International Brotherhood of Teamsters union - which represents some 340,000 UPS employees who sort, load and deliver packages in the United States - are deadlocked.

The Teamsters say if a deal is not ratified before the current contract expires at midnight on July 31, workers will strike.

(Reporting by Lisa Baertlein in Los Angeles, additional reporting by Priyamvada C in Bengaluru; Editing by Pooja Desai and Jonathan Oatis)