The EU says new sanctions against Russia should be adopted shortly and take effect on Tuesday, despite a Kremlin warning of retaliation.
But an EU spokeswoman said the sanctions would be “reversible”, depending on the situation in Ukraine.
Pro-Russian rebels and government troops are observing a fragile truce.
Russia has warned that it could block international flights through its airspace if the EU goes ahead with new measures over the Ukraine conflict.
The pro-Russian separatists have recently made big gains in eastern Ukraine. But a ceasefire agreed on Friday appears to be holding despite some sporadic shooting.
Fighting in the east has killed some 2,600 people since April.
Russia has repeatedly denied accusations by Ukraine and the West that it has been sending troops into Donetsk and Luhansk regions to help the rebels, who want to establish an independent state.
A European Commission spokeswoman said the new sanctions package targeting Russian firms and officials “is due to be formally adopted by member states through a written procedure later today, so the procedure is ongoing”.
“It will then be published in the official journal of the EU, which should happen in the course of tomorrow at the latest as plans currently stand,” she said.
Earlier Russian Prime Minister Dmitry Medvedev warned that Moscow would respond “asymmetrically” to further sanctions.
A Russian airspace ban “could drive many struggling airlines into bankruptcy”, he told a Russian daily.
“If there are sanctions related to the energy sector, or further restrictions on Russia’s financial sector, we will have to respond asymmetrically… For example, restrictions in the transport sector.
“We work on the basis of friendly relations with our partners, and that’s why Russia’s skies are open to flights. But if we are restricted then we’ll have to respond,” he told Vedomosti (in Russian).
Airlines would have to pay far more for fuel if Russia blocked their routes to Asian destinations, and flight times would be longer in many cases.
Last week an EU official told the BBC that further sanctions would deepen the existing measures, affecting Russia’s access to capital markets, dual-use goods which can be used for military purposes, defence equipment and some other sensitive technologies.