In one of the biggest announcements of its kind, Google told its 140,000-plus employees Wednesday that they must be vaccinated against COVID-19 to return to work in the companys offices.

Getting vaccinated is one of the most important ways to keep ourselves and our communities healthy in the months ahead, Sundar Pichai, the CEO of Alphabet, Google s parent company, said in a company-wide email obtained by The New York Times and The Associated Press .

The company also pushed back its planned return-to-office date from September to mid-October, reflecting growing concern about the delta variant of COVID-19.

We recognize that many Googlers are seeing spikes in their communities caused by the Delta variant and are concerned about returning to the office, Pichai wrote. This extension will allow us time to ramp back into work while providing flexibility for those who need it.

Its not yet clear how Google will proceed with employees who refuse to be vaccinated, but Pichai said in his email that, so far, its been encouraging to see very high vaccination rates among Googles workforce in places where the vaccine is widely available. In Santa Clara County, where Googles headquarters is located, 77% of people over age 12 are fully vaccinated 20% higher than the nation as a whole.

While several employers have begun announcing vaccine rules for their staffs, Google may now be the biggest to do so. The company operates more than 70 offices in 50 countries and is one of the most influential brands in the tech sector.

Many conservative lawmakers have pushed back against vaccine mandates, claiming theyre an infringement on personal rights. The argument is a regular fixture on Fox News , where the networks biggest stars have been casting doubt on the vaccine despite widespread evidence that its overwhelmingly safe and effective.

Daily vaccination rates in the U.S. have plummeted . In mid-April, the U.S. averaged 3.4 million COVID-19 vaccines distributed each day, but that number has seen an 80% decrease in recent weeks, dropping to under 590,000 per day despite the vaccine being readily available. Meanwhile, there has been an uptick in new cases of the disease, with the largest concentration of outbreaks in states where vaccination rates are low.