WASHINGTON—A group of 17 U.S. House Democrats on Monday are introducing legislation on Monday that would award $6 billion to the U.S. Postal Service (USPS) to buy tens of thousands of additional electric delivery vehicles. The bill sponsored by Representative Jared Huffman and seen by Reuters would require at least 75 percent of the new fleet be electric vehicles. Last month, the USPS said it was committed to having electric vehicles make up 10 percent of its next-generation fleet as part of its multibillion-dollar plan to retire its 30-year-old delivery vehicles, but could boost that if it received billions of dollars in government assistance. The legislation is backed by some key Democrats, including Representative Peter DeFazio, who chairs the Transportation and Infrastructure Committee, and Representative Carolyn Maloney, who chairs the Oversight and Reform committee that oversees USPS. The bill would also require no less than 50 percent of medium/heavy-duty vehicle …