It’s not a new challenge for manufacturers, but it is one that seems to be getting tougher: finding enough people to fill all the open jobs.

Low unemployment and a surplus of work shouldn’t be cause for concern, but together, they’re adding up to a problem for manufacturers, who have already been struggling to find qualified workers.

There were close to 6.7 million job openings in April, the most recent month for which Bureau of Labor Statistics data is available. Overall, that’s a small increase over March.

But manufacturing was a segment that saw notable growth. For April, the sector had 451,000 openings, about 30,000 more than it had in March and about 78,000 more year over year.

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