According to a friend of mine who owns a truck business, in the East vehicles with Ukrainian plates are being harassed (stopped, questioned, inspected, detained) by Pro-Russian militia members.
I think this is enabled because in the east, the police were all closely tied to the now-deposed Party of Regions. They are demoralized and in disarray.
The power vacuum gives more free reign to Russian militias consisting of Russians rent-a-thugs as well as locals. There has been speculation in the mainstream media that Russian Special Forces are encouraging these militias. I think that’s likely.