NEW YORK — All employers want for Christmas is some holiday help. But they might not get their wish.

Companies that typically hire thousands of seasonal workers are heading into the holidays during one of the tightest job markets in decades, making it unlikely they’ll find all the workers they need. For shoppers, it might mean a less than jolly holiday shopping experience, with unstaffed store aisles and online orders that take longer than usual to fill.

Job openings are already plentiful, allowing job seekers to be pickier about where they work. There were 10.4 million job openings at the end of August and 11.1 million openings the month before, the highest on record since at least December 2000, when the government started recording that figure. At the same time, the Labor Department said that the number of people quitting their jobs jumped to 4.3 million in August, up from 4 million in July.

Even before the holiday hiring season, employers were so desperate to find workers that they raised pay above $15 an hour, started offering four-figure sign-on bonuses and promised to pay their schooling. But that yielded only limited success.

Not having enough workers can be costly for companies. FedEx said it spent $450 million between June and August due to higher wages, paying overtime and other costs related to the tight job market.

At one of its hubs in Portland, Ore., FedEx has about 65% of the staff it needs. The company has been diverting about a quarter of the packages that would normally flow to other hubs farther away that can handle it. More than 600,000 packages a day are being rerouted, leading to worsening service, said FedEx Chief Operating Officer Rajesh Subramaniam President, during a call with investors last month.