The letters were addressed to "the children of satan," and were sent to Evergreen Islamic Center in San Jose, as well as four other mosques since.
The handwritten letters call Muslims a "vile and filthy people."
Zahra Billoo, head of the Bay Area chapter of the Council on American Islamic Relations, says San Jose Police responded very quickly to step up protection of the local mosque, but with five mosques getting the letters now, CAIR is formally asking the FBI to take charge.
"We're making a formal request to federal law enforcement, because at this point, it seems that at least five mosques across the country have received this letter, all sent through the U.S. Postal Service, and so, we want to make sure that all levels of law enforcement are taking this seriously, and looking into this matter," Billoo said.
The FBI held a news conference at one of the mosques targeted in Los Angeles. Billoo says Muslims are entitled to the same First Amendment rights as all Americans, and the president-elect needs to speak much more forcefully against racism, violence and intimidation.
In Los Angeles, Deputy Chief Michael Downing said Monday that police there are investigating two letters received by mosques in the city as a hate incident, but not a crime at this point.
The letter referred to Trump as the "new sheriff in town" and said he would do to Muslims what Hitler did to Jews.
Stephen Woolery of the FBI says the letters are awful, intimidating and harassing. But the FBI is not investigating at this point because they don't pose a specific threat.
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