As senators deliberate over legislation to impose new sanctions on Russia, former government officials warned against any action that would harm European allies that rely on gas imports from Russia.

“It’s very difficult with some of the bills that have been laid out to only punish Russia without punishing our European friends,” said Senate Foreign Relations Chairman Bob Corker, R-Tenn., at a Wednesday hearing on the importance of NATO.

At least three pending Senate bills would impose sanctions on Russia’s energy sector — either to punish it for the 2016 U.S. election interference or to deter it from conducting similar interference in the future. Corker said it’s possible one of the bills to further sanction Russia could pass this fall.

But finding a way to decisively punish and deter Russia — with energy exports that make up an outsize share of its economy — without hurting Europe is a conundrum for Congress, especially since previous rounds of targeted sanctions on Russian individuals have not stopped Moscow’s behavior. Europe relies heavily on imports of Russian natural gas.

Corker’s committee is considering legislation from ranking member Robert Menendez, D-N.J., and Lindsey Graham, R-S.C. that would sanction foreign investment in energy projects supported by Russian state-owned firms. The bill contains provisions dealing with foreign policy, weapons of mass destruction and cybersecurity. The legislation is considered the most likely sanctions vehicle to move this Congress.