Critics of Rex Tillerson pounced on Wednesday when he categorically denied that ExxonMobil lobbied against sanctions placed on Russia or Iran.

"I never lobbied against the sanctions. To my knowledge, ExxonMobil never lobbied against the sanctions," Tillerson said during Wednesday's confirmation hearing for his nomination to be secretary of state.

Democrats quickly seized on the issue, questioning whether Tillerson may have lied under oath.

In a letter reported first by CNN, the Democratic-aligned opposition research group American Bridge 21st Century is asking FBI Director James Comey to investigate whether Tillerson may have perjured himself.

Even Senator Bob Corker, the Republican chairman of the Senate Foreign Relations Committee, seemed to suggest that Tillerson had in fact lobbied Congress about the sanctions placed on Iran.

"I think you called me during this time," Corker said, referring to a conversation he had with Tillerson about Iran sanctions.

Tillerson said Exxon (XOM) participated in discussions about how sanctions were going to be implemented and how they would impact U.S. business interests.

He held steadfast, refusing to concede.

"ExxonMobil did not lobby against the sanctions," he said multiple times.

Surprised lawmakers produced lobbying records suggesting otherwise. Democratic Senator Bob Menendez held up lobbying reports showing Exxon spent millions of dollars to lobby Congress about the sanctions placed on Russia as well as the 2010 Iran sanctions.

For instance, a 2014 lobbying form shows that Exxon lobbied Congress on three different sanctions bills: Russian Aggression Prevention Act of 2014; the Ukraine Freedom Support Act of 2014 and the Sanction Iran, Safeguard America Act of 2014.

"I know you're new to this, but it's pretty clear...There was lobbying here," said Menendez.

Menendez noted that lobbying disclosure forms are not needed when companies are simply seeking information or clarification about a bill. "That's not lobbying. Lobbying specifically is to promote a position," he said.

Tillerson said lobbying forms don't require companies to indicate what side they took.

"I don't know if the forms indicate we were lobbying for the sanctions or against the sanctions," Tillerson said.

Related: Exxon would win if Tillerson works to lift Russia sanctions

However, Menendez countered: "I know you weren't lobbying for the sanctions." In fact, he said: "Exxon became the in-house lobbyist for Russia against these sanctions."

Exxon had every reason to be against those sanctions. Exxon bet billions on a 2011 deal with Russian oil giant Rosneft -- a deal that Vladimir Putin himself appeared to celebrate the signing -- to develop the vast untapped oil resources in the Arctic. Exxon has admitted it may have lost up to $1 billion due to the 2014 sanctions.

Tillerson said it's his understanding that lobbying reports are required whether you are lobbying for or against a given legislation.

"So you believe you were paying lobbyists for sanctions?" Menendez asked incredulously.

Tillerson replied, "I don't know, senator. It would depend on the circumstances."

Exxon put out a statement and a tweet backing Tillerson's testimony.

"As our former chairman said, we provided information about the impact of sanctions, but did not lobby against sanctions," an Exxon spokesperson said. "The lobby disclosure reports do not contradict his testimony and do not say we lobbied against sanctions."

Let's be clear: we engage with lawmakers to discuss sanction impacts, not whether or not sanctions should be imposed — ExxonMobil (@exxonmobil) January 11, 2017

Related: Tillerson's Exxon didn't put America first

Tillerson also said he was unaware of whether Exxon is a member of USA *Engage, a business coalition that has lobbied against sanctions on Iran and other countries.

That's despite the fact that Exxon is listed as a member of USA *Engage on the site's archives. And a spokesperson for USA *Engage confirmed with CNNMoney that Exxon is a member of the group.

In 2014, USA *Engage put out a statement saying "we regret that Congress has legislated additional U.S. sanctions against Russia."