Russia may impose limitations on European airlines flying over Siberia in retaliation for the European Union’s plans to levy fees on carbon emissions by airlines using its airports.

The measure is one of a number of options the government is considering after agreeing with other disgruntled nations to take action against the measures during a two-day summit in Moscow that wrapped up Wednesday.

Twenty-three “unwilling” nations opposed to European carbon levies on airlines that gathered for a two-day summit in Moscow, including the United States, China and India, inked a declaration listing a range of retaliatory measures Wednesday.

The declaration proposes various measures, including sending a formal complaint to the United Nations’ International Civil Aviation Organization, or ICAO, ceasing talks with European carriers on new routes and even levying fines on EU carriers, Reuters reported.

Commenting on possible retaliatory measures, Deputy Transportation Minister Valery Okulov revealed that Russia might limit options for European airlines wanting to increase flights on the trans-Siberian route, favoring Asian airlines instead, Interfax reported.

The country may also follow China in banning its airlines from participating in the emissions scheme and has readied a draft law to that effect, Okulov said.

The Russian government also hinted Wednesday that it may challenge the scheme under the 1944 Chicago Convention, although a previous legal challenge by U.S. and Canadian airlines was thrown out by the European Supreme Court late last year.

But the document lists a range of options, rather than a program for action, avoiding talk of an all-out trade war over the issue.

Okulov told reporters Wednesday that “every state will choose the most reliable measures that will help cancel or postpone” the emissions-trading system.

All airlines using EU airports are required to buy permits from the EU’s emissions trading-scheme under rules introduced at the beginning of this year.

The scheme has sparked outrage in countries including Russia, the United States and China, which have complained that it is anti-competitive and violates international aviation treaties.

Russia says the scheme would cost its airlines 20 million to 25 million euros ($26.6 million to $33.2 million) a year.

All three countries say they support the idea of economic mechanisms to reduce greenhouse gases, but that they must be introduced through multilateral talks within the ICAO, according to comments posted on the ministry’s website.

The Europeans say they acted independently because the ICAO route failed.

European officials reacting to the Moscow declaration Wednesday said they would only adjust or scrap the scheme if an alternative, international scheme was introduced.

“Unfortunately, our question for Moscow meeting participants remains unanswered: what’s your concrete, constructive alternative?” tweeted Climate Commissioner Connie Hedegaard.