The jobs purge sweeping US tech firms has escalated as Amazon expanded staff-cutting plans to affect more than 18,000 workers, The Guardian reported.

Amazon’s reductions are the biggest by a big tech firm over the past year and the largest set of layoffs in the company’s history.

The online retailer’s chief executive cited “the uncertain economy” for the move and said Amazon had “hired rapidly over the last several years.”

Andrew Jassy, Amazon’s CEO, said in a note to employees: “Between the reductions we made in November and the ones we’re sharing today, we plan to eliminate just over 18,000 roles.” It was reported in November that Amazon had planned to cut 10,000 roles.

Jassy said Amazon had weathered “difficult economies” in the past and would continue to do so. “These changes will help us pursue our long-term opportunities with a stronger cost structure.”

He said the layoffs would mostly affect the company’s brick-and-mortar stores, which include Amazon Fresh and Amazon Go, and its PXT organizations, which handle human resources and other functions.

He did not specify where the affected roles were located, but said Amazon would communicate with employees “or where applicable in Europe, with employee representative bodies,” from  January 18.

The layoffs amount to 6% of Amazon’s roughly 300,000 person corporate workforce, and equate to about 1.2% of the company’s global workforce of more than 1.5 million.