Roughly half of all U.S. workers stand to earn more in unemployment benefits than they did at their jobs before the coronavirus pandemic shut down swaths of the U.S. economy, a result of government relief that employers say is complicating plans to reopen businesses.

The package of coronavirus stimulus laws Congress passed and President Trump signed in March included a $600 boost to weekly unemployment benefits through July 31. As that support is added to state benefits over the coming weeks, the average weekly payment to...