According to a report from The Washington Post, Trump adviser and son-in-law Jared Kushner tried to open up a secret and private communication line between the Trump team and the Russian Kremlin. Kushner went so far as to suggest using Russian facilities in the U.S. to conduct the talks so as to avoid monitoring by the U.S. government. This information comes from U.S. officials with access to confidential intelligence reports.
Russian ambassador to the U.S. Sergey Kislyak reportedly told officials in Moscow that Kushner was willing and open to the idea, which the Trump adviser proposed himself on a meeting in the first week of December at Trump Tower. This meeting took place before Trump took office, while he was still the president-elect. U.S. officials became aware of this meeting and Kushner's proposal after reviewing intercepted Russian communications.
The Trump administration did eventually admit that this meeting between Kushner and Kislyak, along with former National Security Adviser Michael Flynn, took place. However, the administration failed to reveal Kushner's proposition for a clandestine communication line.
Now, the FBI is reportedly investigating the meeting and reviewing the legality of it, including whether or not anything Kushner revealed would be a threat to national security. Even Kislyak was reportedly skeptical of Kushner's proposition. If Russia were to allow anyone in the Trump administration to use their communication lines (which Kushner wanted to do to avoid U.S. surveillance), it would pose a direct security threat to both the U.S. and Russia.
Although it is common practice for newly appointed advisers to establish fresh lines of communication with foreign leaders following a U.S. election, Kushner's way of handling said practice raises concerns because of how he went about it. The fact that Michael Flynn was involved with the meeting is also a concern, as he was forced to resign less than a month into his role as national security adviser due to illegal contact with Russia. Furthermore, it is unusual for such direct communication channels to be established before the president-elect officially takes office.