The growth of small businesses in the U.S. was held back in April because small businesses could not find enough workers, the National Federation of Independent Businesss said Tuesday.

“Small business owners are seeing a growth in sales but are stunted by not having enough workers,” said NFIB Chief Economist Bill Dunkelberg. “Finding qualified employees remains the biggest challenge for small businesses and is slowing economic growth. Owners are raising compensation, offering bonuses and benefits to attract the right employees.”

Forty-four percent of small business owners said they had job openings they could not fill, the NFIB said.

The NFIB’s small business optimism index rose 1.6 points to 99.8, undershooting expectations for a rise to 100.8.

Eight of the ten components of the index rose in April. Plans to increase employment and expectations for the economy declined.

Business leaders have been saying that they believe that Americans are being discouraged from returning to the workforce by enhanced unemployment benefits, which allow nearly half of jobless recipients to collect more money than they did while working. President Joe Biden and Treasury Secretary Janet Yellen have repeatedly claimed that is not the case, contrary to mounting evidence.

In April, the U.S. economy added just 266,000 jobs, far fewer than the one million economists had expected.