An increase in scam artists pretending to be government tax agents is being reported in northwest Missouri and soon, according to one Senator, it may be harder to filter out the real collectors from the scammers.

The Livingston County Sheriff’s Office said it is receiving a high number of calls from citizens reporting recent contact by scammers claiming to be from the IRS. The scammers are demanding immediate payment settle a past due balance. The office said some have reported even being told local law enforcement would serve an arrest warrant if they did not comply.

Missouri Senator Clair McCaskill said Tuesday that she is urging the IRS to combat the fraudulent robocalls.

Last year, Congress authorized the use of robocalls for government debt collection. McCaskill said she opposed these efforts, out of concern that such calls would confuse consumers and muddy the agency’s message that the IRS never calls individuals.

“I am concerned that a new program that gives the green light to legitimate and authorized debt collectors will only serve to confuse vulnerable individuals,” wrote McCaskill in a letter to IRS Commissioner John Koskinen. “How will an individual know whether a caller claiming to represent the IRS is a scam artist or a government contractor?”

Currently, law enforcement authorities tell individuals that the IRS does not call.

“The IRS does not work this way. Remember, very little if anything with the Federal government happens fast,” Sheriff Steve Cox said. “If you have fallen victim and sent money it is important you immediately notify your local law enforcement agency.  Otherwise simply hang-up if you receive such a call.”

McCaskill, last year said she led a hearing on preventing phone scams and the IRS impersonation scheme, which officials have called the “largest, most pervasive impersonation scam in the history of the IRS.”

At that hearing, McCaskill said, “If you get a call from the IRS out of the blue, don’t answer it—let it go to voicemail.” The IRS has developed that same consistent messaging, however she said, last winter Congress passed two measures that would upend that message by making it far more likely that consumers might confuse a real IRS call with that of a scammer. Those measures required the IRS to employ private debt collectors, and to allow those debt collectors to use robocalls for debt collection.