(CNN) -- Maricopa County, Arizona, Sheriff Joe Arpaio said Tuesday he shrugged off reports of a $1 million bounty on his head by Mexican drug cartels, saying this is not the first -- nor the largest.
Arpaio, who calls himself "America's toughest sheriff," told CNN he had a $5 million bounty on his head when he worked for the Drug Enforcement Administration in Mexico.
"It's nothing new," Arpaio said on CNN's "American Morning." "It's part of my job. They keep coming after me."
Maricopa County Sheriff's Office spokeswoman Lisa Allen said Monday that authorities are investigating the threat, which came in the form of a text message from a throwaway cell phone in Mexico.
Allen said that the message was sent to a "text message tree," similar to a phone tree. The message offered $1 million to anyone who could kill Arpaio. She said investigators "don't know how likely it is" they will be able to track down the sender.
It was not clear how the threat came to light.
Allen said the FBI is assisting in the probe, but FBI special agent Manuel Johnson, a spokesman for the bureau's Phoenix office, said the agency is aware of the reported threat but he knows of no federal investigation. Johnson said the bureau would help if Arpaio's office requested assistance.
Arpaio is well-known for creating a tent city jail in the Arizona desert, providing pink underwear for inmates and bragging that he spends more to feed his dog than a prisoner in his jail. He made national headlines for his tough enforcement of Arizona's anti-illegal immigration laws and for his outspoken support for a new state immigration law, parts of which were blocked by a federal judge last week.
His critics say he has a long history of abusing his power and launching bogus criminal investigations against political opponents. Those critics note that while the probes were launched with great public fanfare, they rarely resulted in convictions.
A federal grand jury is probing the complaints, but Arpaio's allies have defended the investigations as necessary. The 78-year-old sheriff, who has been the chief law enforcement officer for the county that includes Phoenix and many of its suburbs since 1992, would not discuss the issue with CNN in a July interview, citing the federal probe.
Arpaio was elected Maricopa County sheriff in 1992 and has been re-elected every four years since. He served for 32 years in federal law enforcement before then, ultimately becoming head of the DEA's Arizona office.
Speaking Tuesday on "American Morning," Arpaio said the latest threats come with the job.
"It's part of my work," he said. "I do my job. Nothing changes."