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Amber Portwood allegedly threatened the YouTuber who posted clips of her machete incident with her baby daddy ... and that could get her in big trouble with her probation officer.

The Marion County District Attorney tells TMZ ... Katie Joy -- the woman behind a YouTube account that's been documenting Amber's domestic violence case -- reached out to the D.A.'s Office and accused Amber of making threats.

We're told the D.A. passed it along to the probation officer overseeing the "Teen Mom OG" star's case. As we've reported, Amber pled guilty to 2 felonies -- domestic battery and intimidation. She got 906 days of probation, but if probation is violated the judge can send her to the slammer for a long time.

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In this clip from Amber's Instagram Live ... Katie claims Amber's speaking directly to her, when she says, "I know your address." Portwood says someone is going to get what she has coming to her, and Katie claims Amber's clearly referencing her.

Remember ... Katie's YouTube account, Without a Crystal Ball, published video and audio of the entire blowout between Amber and Andrew Glennon.

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Sources close to Katie tell TMZ ... she's getting threats from Amber's fans hoping she dies, and she's afraid one of Portwood's fans will attack her.

We're told Katie has not filed a police report because she's not sure what cops in Minnesota -- where she lives -- would be able to do.