By Jason Lange

WASHINGTON (Reuters) - A U.S. federal agency on Saturday said it could start issuing citations to companies as soon as January 10 for failure to comply with a nationwide mandate that they either vaccinate or test regularly for COVID-19, as a U.S. Supreme Court showdown over the policy looms.

The announcement came one day after a U.S. appeals court reinstated the Biden administration policy that requires large businesses to verify employees are vaccinated against COVID-19 or submit to weekly testing.

Another court in November had blocked the rule from the Occupational Safety and Health Administration (OSHA), and the legal battle is expected to continue to the Supreme Court.

On Saturday, OSHA said it would not cite companies for any kind of noncompliance with the rule before Jan. 10 "to provide employers with sufficient time to come into compliance." OSHA also said citations around COVID-19 testing would not begin before Feb. 9.

The OSHA rule applies to businesses with at least 100 workers and covers 80 million American workers.

The rule has triggered a significant backlash, particularly in Republican-leaning states. Republicans hope to make popular frustration with COVID-19 safety measures a central theme in political campaigns ahead of the November 2022 congressional elections, when Republican hope to seize control of Congress.

President Joe Biden has argued the vaccine mandate is essential for fighting the pandemic, which has killed more than 800,000 Americans and weighed on the economy.

Biden will announce new steps for fighting the pandemic on Tuesday, a White House spokesperson said.

The debate coincides with public health officials bracing for a "tidal wave" of coronavirus infections in the United States as the more transmissible Omicron variant spreads rapidly worldwide.

(Reporting by Jason Lange; Editing by David Gregorio)