CHICAGO, Aug 26 (Reuters) - Tyson Foods (TSN.N) said on Thursday it is offering U.S. chicken plant workers the chance to win $10,000 once a week for the next five weeks if they have received at least one dose of a COVID-19 vaccine. The vaccine lottery is the latest attempt to encourage vaccinations by the country"s biggest meat company by sales, as the contagious Delta variant of the coronavirus drives an increase in U.S. cases. Tyson employees at nearly 50 chicken facilities are eligible for the prizes, spokesman Derek Burleson said. The company on Aug. 3 mandated that all employees be vaccinated by Nov. 1, though the requirement for unionized plant workers is subject to negotiations with labor unions. read more At that time, about 56,000 employees had already been vaccinated, roughly 47% of Tyson"s U.S. workforce of 120,000, according to the company. read more Tyson said on Thursday that discussions with union leaders on the mandate are ongoing. "We"re already in alignment on the need to continue doing everything we can to protect our team members from the health impacts of the COVID-19 virus," Burleson said. Tyson is also paying $200 to any employee who gets vaccinated and compensating workers for up to four hours of regular pay if they are vaccinated outside normal work hours or away from a Tyson location, according to the company.