That mass return to offices in September is looking like less of a sure thing.

Apple has pushed back the date when it expects the majority of its office-using employees to return to in-person work from September to at least October, Bloomberg reports. In setting the original September return date, Apple CEO Tim Cook cited the broad availability of coronavirus vaccines and declining case counts.

While vaccines remain plentiful across the U.S., skepticism and outright refusal to be vaccinated have combined with the highly contagious delta variant of the coronavirus to drive case numbers back up virtually everywhere in the country, in addition to spikes being experienced abroad.

The average number of new daily coronavirus cases in California, where Apple is headquartered, has tripled in the past two weeks, The New York Times reports. Santa Clara County, which contains Apple's home city of Cupertino, has returned to recommending indoor mask-wearing for vaccinated and unvaccinated people. It isn't alone, either: Los Angeles and Las Vegas have issued similar advisories, and some counties across the country are beginning to reinstate mask mandates, Barron's reports.

The delta variant has dampened optimism for an economic recovery based on stock market performance. The S&P 500 dropped the most it has in two months on Monday, Bloomberg reports.

Companies that attempt to stick to September reopening targets face increased risk of worker revolts and potential legal action, as individuals with disabilities and pre-existing conditions that would exacerbate the effects of Covid-19 have been filing discrimination lawsuits against employers that have demanded that they return to the office, Bloomberg Law reports.