MIAMI (AP) — Nearly one year after receiving powerful new authority to impose moratoriums that would prevent potentially fraudulent Medicare providers from joining the program, federal health officials have yet to impose a single one, according to top Senate Republicans.

Under the Affordable Care Act, the Centers for Medicare and Medicaid Services was granted broad power to impose moratoriums in regions where fraud is rampant or for certain types of providers such as medical equipment or home health care, sectors where billions of Medicare fraud dollars have been lost. Teams of federal prosecutors and health investigators have set up camp in nine fraud hot spots around the country including Miami, Brooklyn, Detroit, Houston and Los Angeles — all obvious places to consider moratoriums.

Yet federal health officials inexplicably have not done so, according to Senators Chuck Grassley of Iowa and Orrin Hatch of Utah, both ranking Republicans on the Senate Finance and Judiciary Committees. The senators sent a letter to federal health officials Tuesday urging them to use moratoriums as a tool to combat an estimated $60 billion a year in Medicare fraud.