Throughout its existence, states were prohibited from charging tolls on Interstate Highways built with federal funds, with only certain East Coast highways allowed to continue collecting tolls when they were grandfathered into the Interstate System. In recent years, the federal government has relaxed certain prohibitions so that states could fund new Interstates and even rehabilitate existing ones through tolls. However, a trade association representing toll road operators is asking Congress to completely lift the ban on tolling Interstates, which would yield new opportunities for their craft. Other organizations have also pushed for the elimination of the ban as a means to address deficiencies. Critics argue that tolling is a form of double taxation, since the highways themselves were built with gas tax revenues.