Almost 1,000 staff at packaging producer DS Smith voted to strike over pay in a move their union said will affect clients of the United Kingdom firm including Amazon.com Inc. at one of the busiest times for retail purchases.

Employees at five DS Smith sites across Britain could walk out before the end of this month, according to an emailed statement from the GMB union, which said that 93% of members had backed industrial action.

Amazon may face a shortage of packaging when fulfilling orders from the Black Friday shopping period as a result of the dispute, the GMB said. Other DS Smith customers include drinks giants PepsiCo Inc. and Diageo Plc, McVities biscuits and KP snacks, it said.

“A strike at DS Smith could have serious implications across a range of household names, not least Amazon, which gets packaging from the company,” GMB National Officer Eamon O’Hearn said in the release.

The strike ballot was held after DS Smith proposed a 3% salary increase plus a £760 payment for 2022-2023, according to the union. The offer represents a “massive real terms pay cut” with UK inflation in double figures, the union says.

A spokesperson for DS Smith said the company was “disappointed” with the strike threat especially as it came at a “crucial time” for customers. DS Smith added that contingency plans were in place and that negotiations were ongoing.

Amazon didn’t immediately respond to requests for comment.

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