Companies across the United States are revising their back-to-office plans, driven by rising uncertainty around the omicron COVID-19 variant that has pushed up infections to record levels in the world's biggest economy.

U.S. financial firms were among the first to encourage employees to return to offices, but rising cases have forced most of the major banks to rethink their plans and tighten vaccination mandates.

Here is a list of companies that have taken new actions as omicron cases have risen:

Meta Platforms Inc. has delayed its office reopening to March 28 from Jan. 31; mandates booster jabs for workers returning to office.

Alphabet Inc. has postponed its January return-to-office plan globally for an indefinite period of time.

Amazon.com Inc. has shortened isolation to one week from 10 days for those testing positive for COVID-19 after updated guidance from the Centers for Disease Control and Prevention (CDC).

Starbucks Corp. will require U.S. workers to be fully vaccinated against COVID-19 or undergo weekly testing.

Walmart Inc. has reduced paid leave for workers testing positive for COVID-19 to one week from two weeks after updated CDC guidance.

Kroger Co. will stop providing paid COVID-19 leave for unvaccinated employees and will apply $50 monthly health insurance surcharge to salaried non-union workers who are unvaccinated.

Chevron Corp. has postponed a scheduled January full return to office for its two largest U.S. work sites; did not specify new return date.

Bank of America is offering its workers on-site vaccine booster clinics, bu tis encouraging employees to work remotely.

Citigroup will begin implementing a "no-jab, no-job" policy for employees starting Jan. 14, unless they have been granted an exemption.

Goldman Sachs is encouraging all eligible U.S. staff to work from home until Jan. 18, while its offices will continue to remain open with previously announced COVID-19 safety protocols.

JPMorgan Chase & Co. is offering its staff the option of working from home for the first two weeks of 2022, with a caveat that all employees are expected to return to office no later than Feb. 1.

Morgan Stanley has asked employees, contractors and visitors to show proof of vaccination before entering its New York headquarters.

Wells Fargo & Co. has delayed its plans for employees to return to the office "given the changing external environment."

Jefferies is requesting its staff to work remotely until Jan. 31, according to a post on Instagram from the investment bank's chief executive officer.

Ford Motor Co. says it will extends its hybrid return-to-work plan through March as the state of the COVID-19 pandemic remains uncertain.