The US State Department has announced that they intend to soon impose additional sanctions against Russia, after demanding that Russia provide them with a statement offering very specific “assurances” on the use of chemical weapons.
This all goes back to the allegations of a March Novichok attack in Salisbury, England. The British government blamed Russia for the attack, while Russia has denied it. The US already sanctioned Russia over the matter, and expelled large numbers of Russian diplomats.
They followed this up by demanding Russia give the US “reasonable assurances” that they will never again use chemical weapons. Russia never did so, since these assurances were predicated on Russia accepting guilt for the attack they denied involvement in.
It is unclear when the new sanctions will take effect, but Russia is warning that using this as a pretext for new US sanctions and other restrictions would be illegal. In Congress, many are pushing the State Department to impose massive sanctions against Russia, though this is a general trend and not necessarily based on any belief Russia launched this specific attack.