Google is implementing a new Covid-19 testing policy for its U.S. work sites as it prepares for a continued surge in infections from the Omicron variant in the coming weeks.

In an email sent to full-time employees on Thursday and obtained by CNBC, Google’s health chief Karen DeSalvo said anyone who comes into contact with a Google office or facility will require a negative molecular test. They should also report their vaccination status and wear surgical-grade masks while at the office, the memo said.

“The Omicron variant has become the dominant strain in then U.S. and is highly transmissible,” DeSalvo wrote. “There has been a significant rise in infection across the country, and hospitals are overwhelmed with COVID patients — reducing their capacity to provide care to others who need it.”

Google has been more aggressive of late than its tech peers in enforcing Covid-19 safety measures among workers. Last month, the company told employees that they must comply with vaccine policies or face losing pay and eventually losing their job. That marked a shift by executives, who just a few months earlier said the company would not mandate vaccines.

Several hundred Google employees signed and circulated a manifesto opposing the company’s widened Covid-19 vaccine mandate.

When it comes to testing, Google has been preparing for a moment like this. In April, Google started providing at-home Covid-19 tests from Cue Health to employees. It’s the testing company’s biggest private sector customer.

Four months later, Google’s cloud division entered into a separate agreement with Cue to develop real-time variant tracking and sequencing of Covid-19, a partnership that gives Google unique access to testing and variant data.

“We expect this to continue over the next few weeks,” DeSalvo wrote, adding that the new testing rule is temporary. “During this period of heightened risk, we are making it a matter of policy to get a weekly molecular test (e.g. PCR, Cue) if you are coming into the office.”

DeSalvo reminded employees that Google offers free at-home and in-person viral testing options to both full-time staffers and the extended workforce, which includes temps, vendors and contractors. A recent report by Bloomberg said Google’s extended workforce had longer wait times for test results compared to full-time workers.

In an email to CNBC, a Google spokesperson said the company is “implementing new temporary health and safety measures for anyone accessing our sites in the US,” and is putting policies in place to make “workplaces and communities as safe as possible.”

DeSalvo said the molecular tests will help alleviate pressure on clinics, schools and pharmacies, which have struggled to keep rapid antigen test supplies in stock.

Google has more than 150,000 full-time employees and nearly the same amount of contractors and vendors. As of mid-December, executives said the company had so far opened 90% of its U.S. offices and, in recent weeks, nearly 40% of its U.S. employees went to a facility at some point.

Google had been expecting its workforce to return to physical offices starting in January, but it pushed back its plans last month, citing concerns around infection rates. However, executives didn’t name Omicron at the time and still encouraged employees to continue coming in “where conditions allow.”

While Google is strengthening its mandates, federal rules appear to be going in the opposite direction. The Supreme Court on Thursday blocked the Biden administration from enforcing its sweeping vaccine-or-test requirements for large private companies. The mandate required that workers at businesses with 100 or more employees get vaccinated or submit a negative Covid test weekly to enter the workplace with a deadline of Jan. 18.

Google executives have used the federal requirements as an explanation for enforcing its internal policies, arguing that the company’s extensive work with the government means everyone must comply regardless of whether they come into the office.

Google told employees in December that those who haven’t complied with the vaccination rules by Jan. 18, will be placed on “paid administrative leave” for 30 days. After that, they’ll be put on “unpaid personal leave” for up to six months, followed by termination.

DeSalvo’s note added more specific directions on safety in light of the Omicron surge.

She advised employees to use a non-cloth or “high quality surgical mask.” She also said they should stay home if they’re not feeling well, even if “it’s just allergies.” DeSalvo recommended employees test as close as possible to the time of an event or office appearance.

“You may not be showing any symptoms, but you could still be spreading Covid-19 to others,” she wrote, adding that vaccinated employees should get their booster “as soon as possible” if they haven’t already.

WATCH: Google employees to lose pay and eventually their jobs if they don’t follow vaccination rules