https://consumerist.com/2017/10/13/states-sue-trump-administration-for-halting-7-billion-in-cost-sharing-payments-to-insurers/

With a one-paragraph statement released late in the evening on Thursday, President Trump announced he was pulling the plug on $7 billion a year in payments from the federal government to insurance companies who sell individual policies through the exchanges set up by the Affordable Care Act. Today, at least five states say they are suing to keep these subsidies in place.

The monthly payments, known as cost-sharing subsidies, are part of the 2010 Affordable Care Act and are intended to keep out-of-pocket expenses — like co-pays and deductibles — low, particularly for Americans making between 100% and 250% of the federal poverty line.