Dec 14 (Reuters) - U.S. workers with severe cases of COVID-19 may be covered by a law prohibiting disability discrimination in the workplace, while milder cases would not qualify, according to guidance issued on Tuesday by the agency that enforces the law. The Equal Employment Opportunity Commission (EEOC) in the guidance posted on its website said COVID-19 cases that persist for more than a few weeks, and impairments caused by the illness, can be considered "disabilities" under the Americans with Disabilities Act (ADA). But, the agency cautioned that whether the law applies to individual workers must be determined on a case-by-case basis. The ADA protects workers from being fired or facing retaliation because of their disabilities. The law also requires employers to offer reasonable accommodations that would allow workers with disabilities to do their jobs. The EEOC in its guidance said asymptomatic and mild cases of COVID-19 are not disabilities under the ADA because they do not limit workers" bodily functions or life activities, such as walking and lifting, for prolonged periods of time. But the law does apply to "long COVID," in which symptoms can persist for months after an initial infection, the commission said. The EEOC also said that employees who seek workplace accommodations can be required to provide documentation to their employers, such as notes from doctors outlining restrictions. The guidance comes as many states and cities are imposing stricter mask-wearing and vaccine mandates amid a winter surge in COVID-19 cases and the spread of the Omicron coronavirus variant.