There is no way to stop the calls from being initiated.  These people are hard core scammer/extortionists located in India and as such beyond the reach of US Law.   Call blocker is your best bet.

Received suspicious call from caller with foreign accent threatening legal action.  Ignored this obvious scam.

Left threatening message about significant law trouble. Totally a scam!

This ridiculous voice message was left on my voice mail and since when does the government make phone calls or better yet work on the weekends or nights.... haha... that's a good one. If a government agency is trying to get a hold of you, they will send you a letter and a number of them before reaching out via the phone. For Scammers VOIP is cheap, doesn't even cost them a stamp to contact you:

Hi, This message is intended to contact you. My name is Steve Martin, and I'm calling regarding an enforcement action executed by US Treasury that needs your immediate attention especially. Ignoring this will be an intentional second attempt to avoid initial appearance before a magistrate judge or a grand jury. For a federal criminal offense. My number is (213) 293-3590. I repeat (213) 293-3590. I advise you to cooperate with us and help us to help you. Thank you.

Also got I call form this a**hole, claims the same thing as everyone else has posted. Im reporting him to every government agency and making sure this a hole gets put away.