According to Release International, which supports persecuted Christians around the world, evangelical churches are being put under restrictions in Crimea, and some Christian leaders fear they will lose their religious freedom if the Russians take control of their country.
It's claimed some church leaders have been accused of being American spies, church buildings have been confiscated and some Christians have even been killed.
Release partner Paul (not his real name) is a church planter in the region. He's warning the situation will only get worse if the separatists gain more ground.
In the Crimea, which was annexed by Russia a year ago, Ukrainian church leaders are said to have been ordered to accept Russian citizenship. Those who refuse are barred from leading their churches.
He said: "In the course of the time, the freedom for the Church started to shrink. Now the situation is totally different.
"The only place of the former Soviet Union where we have the full freedom is the Ukraine.
"In the Eastern part of the Ukraine, which is occupied they see evangelicals as very dangerous people who are linked to western countries. They are regarded as enemies of people and state."
Listen to Paul speaking to Release International's Andrew Boyd: