The Federal False Claims Act makes it illegal to do what?

Makes it illegal to submit a falsified bill to a government agency.

The False Claims Act was enacted in 1863 in response to widely prevalent, massive, defense procurement fraud, in which defense contractors were billing the government for subpar services and goods. The False Claims Act allowed private citizens with knowledge of such fraud being perpetrated on the government, to come forward to share their knowledge in litigation against the fraudsters, and also share in the recovery of any money.