Two Irish diplomats from the embassy in Moscow have been asked to leave Russia.
The Department of Foreign Affairs says the Irish ambassador was summoned to the Russian Foreign Ministry on Thursday afternoon.
Ambassador Brian McElduff was informed that two diplomats from the embassy have been asked to leave.
In a statement, Foreign Minister Simon Coveney says: "There is no justification for the taking of this measure.
"The staff at the embassy of Ireland in Moscow do not have, nor are engaged in, any duties or functions which are incompatible with their diplomatic status."
He adds: "This decision to reduce the size of our relatively small embassy in Moscow will significantly reduce our ability to provide services to our citizens in Russia and to maintain diplomatic channels of communication with the Russian Federation."
The statement did not elaborate on reasons for the expulsion.
It follows a similar move by Ireland last month, when four Russian diplomats were told to leave the country.
The Department of Foreign Affairs said activities by the four officials had "not been in accordance with international standards of diplomatic behaviour".
At the time the department said the Government continues to believe that diplomatic channels between Ireland and the Russian Federation should remain open.