The Electronic Product Environmental Assessment Tool (EPEAT) certification is required under a law passed in 2009 if a federal government agency is to buy goods or services from a company. It ensures that the products meet minimum environmental protection standards.
It is not clear why Apple withdrew from the ratings service, especially as it cuts off sales to a fairly substantial customer — the US Government. One report by the iFixit blog suggested that the problem relates to the difficulty of repairing Apple products and stripping them down for recycling.
Apple has struggled with its eco-friendly credentials, with repeated reports from agencies such as Greenpeace criticizing the company, not just for what they know the company is doing, but also for their apparent secrecy about the environmental impact of their various manufacturing processes.