WASHINGTON, Oct 19 (Reuters) - Three unions representing workers at Union Pacific Corp (UNP.N) filed lawsuits against the U.S. railroad operator"s move to make vaccines mandatory for its 31,000 employees under a deadline imposed by the Biden administration for federal contractors. Union Pacific said on Monday it filed suit against the unions on Friday, saying the action was necessary to prevent any disruption of its rail network "and to avoid any impact on America’s supply chain, as it continues to recover from the pandemic." Union Pacific asked a judge to "have any dispute over the mandate resolved through the various dispute resolution procedures outlined in the Railway Labor Act." The lawsuits were filed in U.S. District Court in Northern Illinois. The union lawsuits said workers who were vaccinated would be paid a $300 incentive and that Union Pacific did not engage union officers or attempt to engage in any bargaining over the matter before imposing the mandate. President Joe Biden signed an executive order on Sept. 9 requiring federal contractors to mandate vaccinations and the White House said on Sept. 27 that millions of employees from covered federal contractors must be vaccinated by Dec. 8. Numerous federal contractors have said they will comply with the Dec. 8 deadline, including Boeing Co (BA.N), American Airlines (AAL.O), Southwest Airlines Co (LUV.N) and International Business Machines Corp (IBM.N).