OYONNAX, France — Along a vast alpine plain, hundreds of factories are cranking out plastic perfume bottles, automobile parts and industrial tools. Trucks chug through mountains ferrying thousands of ready-made wares for export. On billboards and warehouses, “We’re hiring!” signs flutter in the breeze.

Jobs are plentiful in Ain, a sprawling manufacturing region in eastern France known as “Plastics Valley.” But companies in this forested frontier across from Switzerland have slowed production because they cannot find enough workers for a production line that increasingly requires computer and digital know-how.

“It’s a brake on competitiveness,” said Gilles Pernoud, the president and chief executive of Groupe Pernoud, whose company makes injection molding for plastic parts for BMW and other automakers. He said he has turned away contracts worth nearly a million euros in the past two years because he couldn’t find skilled people here or anywhere in France who wanted a factory job.