Moscow has declared 18 members of the EU delegation in Russia “persona non grata”.
The staff members “will have to leave the territory of the Russian Federation in the near future,” the foreign ministry said in a statement.
Responding, the EU said it “deplores the unjustified, baseless” order, adding there were “no grounds for Friday’s decision by the Russian authorities beyond being a pure retaliatory step”.
Dozens of Russian diplomats have been expelled by EU countries over the past month.
At the end of March, Ireland, Belgium, the Netherlands and the Czech Republic issued coordinated orders to expel a total of 43 Russian embassy staffers suspected of spying.
And on 5 April, the EU ordered 19 Russians to leave host nation Belgium for “engaging in activities contrary to their diplomatic status”.
Russia has tended to respond to such decisions with reciprocal action.