Dec 6 (Reuters) - Ford Motor Co (F.N) said on Monday it would push its return-to-work hybrid plan to March as the state of the COVID-19 pandemic remained uncertain. The No. 2 U.S. automaker said it will begin a pilot phase for select employees in February and March. The company had previously said it would not return to work under a hybrid work model - a combination of on-site and remote working - before January. Ford had required most of its U.S. salaried employees to be vaccinated against COVID-19 by Jan. 4.The state of COVID-19 virus remains fluid, and despite the success of our ongoing safety protocols and increased vaccination rates, we are shifting the start date of the hybrid work model to March," Ford said in an emailed statement. This covers Ford"s non-site-dependent employees and does not include plant workers represented by the United Auto Workers union. The union and Detroit Three automakers have recommended vaccinations and boosters for those workers, but those are not mandatory. Wearing masks to curb the spread of COVID in plants remains mandatory, however.Companies are beginning to consider changes to their return-to-office plans and work models overall for employees because of the emergence of the new coronavirus variant, Omicron. Companies are struggling to understand how the variant might affect their operations and profits, with many taking a wait-and-see stance as they assess its spread and potential harmfulness. read more Last week, Alphabet Inc"s(GOOGL.O) Google said it was indefinitely pushing back its January return-to-work office plan globally amid concerns over Omicron and some resistance to company-mandated vaccinations. read moreGeneral Motors Co (GM.N) said Monday it had not yet set a formal return to workplace date for salaried employees. In April, it put in place "Work Appropriately," a plan under which "teams have the flexibility to work where they can have the greatest impact." The largest U.S. automaker said "in light of the Omicron variant, we are monitoring the situation closely and continue to engage with multiple internal and external stakeholders." GM has not yet mandated vaccines for its salaried employees. Stellantis NV(STLA.MI), which is requiring all of its 14,000 U.S. salaried non-represented employees to be fully vaccinated by Jan. 5, said Monday the company was moving "to a flexible and agile work environment that enables our team to meet the challenges and opportunities that lie ahead." Dubbed the "New Era of Agility" pilot program for North America, it is expected to begin in early 2022. Stellantis plans a hybrid working model, with employees spending about 70% of their time working remotely and 30% in offices.