The U.S. Postal Service will ask Congress to slash its work force by 20 percent and change its union health and pension benefits to keep the mail system from going broke next month, The Washington Post reported. Besides cutting 100,000 jobs through attrition, another 120,000 workers would get the ax through buy-outs and layoffs, according to a leaked Postal Service plan. “The Postal Service is facing dire economic challenges that threaten its very existence,” the mail carrier’s higher-ups wrote in a notice to workers. “If the Postal Service was a private sector business, it would have filed for bankruptcy and utilized the reorganization process to restructure its labor agreements to reflect the new financial reality.” Unions vowed to fight the proposal.