Pressure is mounting on Koch Industries, the conglomerate run by the rightwing billionaire Charles Koch, to pull out of Russia after it was revealed it was continuing to do business in Russia through three wholly-owned subsidiaries.

Hundreds of companies including Coca-Cola, KPMG, McDonald’s, Netflix and Starbucks have paused operations in Russia following its invasion of Ukraine. But, as news site Popular Information revealed last week, three Koch subsidiaries are still operating in the country.

“Koch Industries is shamefully continuing to do business in Putin’s Russia and putting their profits ahead of defending democracy,” the Senate majority leader, Chuck Schumer, and Senator Ron Wyden, said in a joint statement. “As the democracies of the world make huge sacrifices to punish Russia for Putin’s illegal and vicious invasion of Ukraine, Koch Industries continues to profit off of Putin’s regime.”

“It must stop,” Schumer wrote on Twitter, adding that he and Wyden were “exploring legislation to add Russia to existing laws denying foreign tax credits for taxes paid to North Korea & Syria.”

Koch has defended its Russian operations. The company has three subsidiaries still operating in the country: Guardian Industries, a glass manufacturer; Molex, an electronic components manufacturer; and Koch Engineered Solutions, a provider of industrial products.

In a statement released on Wednesday Dave Robertson, Koch president, condemned the invasion. “The horrific and abhorrent aggression against Ukraine is an affront to humanity,” he wrote. But he said the company would not “walk away” from its employees.

“Koch company Guardian Industries operates two glass manufacturing facilities in Russia that employ about 600 people. We have no other physical assets in Russia, and outside of Guardian, employ 15 individuals in the country. While Guardian’s business in Russia is a very small part of Koch, we will not walk away from our employees there or hand over these manufacturing facilities to the Russian government so it can operate and benefit from them (which is what the Wall Street Journal has reported they would do). Doing so would only put our employees there at greater risk and do more harm than good,” he wrote.

Robertson said the company was “complying with all applicable sanctions, laws and regulations” and would continue to monitor the situation.

The statement was released on the same day that the Ukrainian president, Volodymyr Zelenskiy, made an address to Congress. “All American companies must leave their market immediately because it is flooded with our blood,” said Zelenskiy.

The Kansas-based conglomerate – the second-largest private company in the US – is one of 40 companies “digging in” and refusing to leave Russia, according to a tally compiled by the Yale professor Jeffrey Sonnenfeld and his research team.

Popular Information also revealed last week that a network of pundits and groups funded by Koch has been publicly advocating against imposing economic sanctions on Russia.