Amazon.com's Prime Day sales were lower on the first day said Momentum Commerce. The company which manages online sales for 50 brands said its Amazon sales plunged 41% on Tuesday when compared with the start of Prime Day last year.

Warehouse workers and union representatives said Prime Day meant extra hours in sometimes sweltering temperatures and a heightened risk of injuries.

Prime Day shopping events to entice cautious consumers and play defense against stiffer competition from the likes of Walmart Inc., Target Corp. and TikTok, who have launched their own discount days in response.