(CNN) The FBI will brief Florida members of Congress next week about the claim that a Florida county was hacked by Russian intelligence in 2016, two sources familiar with the plan told CNN.

Previous reporting and government announcements have established that the GRU, Russian military intelligence, created an email phishing campaign aimed at Florida county election employees in the summer preceding the 2016 presidential election. But it wasn't until special counsel Robert Mueller's report was published that the public learned the FBI had investigated a particular county for actually being hacked.

"[T]he FBI believes that this operation enabled the GRU to gain access to the network of at least one Florida county government," the report claims.

The briefing will take place on May 16. The news was first reported by Politico.

During Russia's multi-pronged election interference campaign of 2016 the GRU targeted VR Systems, an electronic pollbook manufacturer that a number of Florida counties use to maintain their voter registration databases. The GRU hackers then sent out phishing emails from Gmail accounts with VR Systems in its name, and with a malicious file attached to more than 120 county election officials.

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