Senate Foreign Relations Committee ranking member Bob CorkerRobert (Bob) Phillips CorkerHillicon Valley: Experts worry North Korea will retaliate with hacks over summit | FBI works to disrupt Russian botnet | Trump officials look to quell anger over ZTE | Obama makes case for tighter regs on tech Senate GOP sounds alarm over Trump's floated auto tariffs Biden, Corker honored with Freedom House human rights awards MORE (R-Tenn.) called on President Obama to impose more sanctions on Russian companies to deter Russian military intervention in Ukraine.

Corker sent Obama a letter over the weekend, ahead of a European Union meeting on Russian sanctions Monday.

“Rather than wait for a Russian invasion of eastern Ukraine to implement additional sanctions, which seems to be U.S. policy at the moment, we must take action now that will help prevent this worst-case scenario before it becomes a reality,” Corker wrote. “Our European allies need to see action, leadership, and resolve from the United States.”

After Russia annexed Crimea, Congress passed a bill sanctioning Russian leaders involved in the military intervention and provided $1 billion in loans to Ukraine in an effort to protect its sovereignty.

Lawmakers have called for additional action as Russian President Vladimir Putin stations troops along the eastern border of Ukraine.

“Unless Russia ends its destabilization of eastern Ukraine and drastically reduces troop levels on the Ukrainian border immediately, further sanctions against strategic sectors of the Russian economy, particularly targeting Gazprom and additional important financial institutions, should be imposed within days,” Corker wrote. “A failure to respond to Russia’s recent actions will give the Kremlin a license to continue to threaten and undermine Ukraine, Moldova, and other countries in Europe and Eurasia.”