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 rise:

Meta Platforms Inc. -- Delays office reopening to March 28 from Jan. 31, mandates booster jabs for workers returning to office

Alphabet Inc. -- Delays January return-to-office plan globally for an indefinite period of time; temporarily mandating weekly COVID-19 tests for those entering Google offices or facilities in the United States

Amazon.com Inc. -- Shortens isolation to one week from 10 days for those testing positive for COVID-19 after updated guidance from the CDC

Starbucks Corp. -- Suspended COVID-19 vaccine-or-test requirement for U.S. employees after Supreme Court ruling, but strongly encourages vaccinations and boosters as well as disclosure of vaccination status

Walmart Inc. -- Reduces 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

General Electric Co. -- Suspended COVID-19 vaccine or test requirement for employees after the U.S. Supreme Court's ruling

Chevron Corp. -- 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 -- Offers on-site vaccine booster clinics, encourages employees to work remotely

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

Goldman Sachs -- Told employees they could delay returning to office to Feb. 1 after having previously allowed workers to work from home until Jan. 18

JPMorgan Chase & Co. -- Offers 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 -- Asks employees, contractors and visitors to show proof of vaccination before entering its New York headquarters

Wells Fargo & Co. -- Delays plans for employees to return to the office "given the changing external environment"

Jefferies -- Asks 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 push return-to-work hybrid plan to March as the state of the COVID-19 pandemic remained uncertain