WASHINGTON—The number of applications for the H-1B visas used by high-tech companies and others to bring highly skilled workers to the U.S. dropped this year after years on the rise, the government said Monday.

It is unclear exactly why, but experts pointed to Trump administration promises to crack down on the abuses in the program, discussion of tougher vetting of foreigners and business decisions by the Indian outsourcing firms that are heavy users of the program.

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