WASHINGTON ― Rex Tillerson, President-elect Donald Trump’s nominee for secretary of state, endangered Christians in Iraq in 2011, a top House Democrat argued in a Tuesday night letter.

The allegation is a serious one, given that many lawmakers ― including most Republicans ― frequently bemoan the plight of Christians in the Middle East.

Rep. Jan Schakowsky (D-Ill.) wants legislators on the Senate Foreign Relations Committee to press Tillerson on the issue in committee hearings on his confirmation this week. The former Exxon Mobil chief executive threatened the heartland of Iraqi Christians ― who are split among various groups, including Assyrians, Chaldeans and Syriacs ― when his company negotiated a 2011 oil deal, she wrote in a letter to the committee’s chair and ranking member.

“The number of Christians in Iraq has declined from 1.2 million residents in 2003 to less than 250,000 today,” Schakowsky wrote. “The deals Mr. Tillerson signed exacerbated an already perilous situation for those beleaguered communities. He helped further marginalize the Assyrian/Chaldean/Syriac Christians and embolden the territorial expansion into their ancestral homeland ― all with neither consent or input from nor compensation to the indigenous communities of the Nineveh Plain.”

She wants senators to ask Tillerson about his knowledge of the deal, whether he believes U.S. policy should protect such minorities and how he plans to shield these communities “from private companies and governments who put profit over human safety and security.”

Read the full letter here.

The oil executive’s 2011 agreement to develop six northern Iraqi oilfields has long been controversial because it undercut U.S. policy on Iraq. By signing a deal with officials in the country’s semi-autonomous Kurdistan region rather than the central Iraqi government, Exxon boosted the Kurds’ claim that they are stable enough to have their own separate country.

The Iraqi Kurds are trusted U.S. partners, but American experts worry that their region becoming independent could force the U.S. to pick between Kurdistan and Iraq, worsen ethnic and sectarian tensions in the area and leave the remainder of the country more vulnerable to Iranian dominance. American officials saw the oil company’s move as unhelpful and selfish. When he learned of the Exxon-Kurdistan deal in November 2011, James Jeffrey, then the U.S. ambassador to Iraq, “dropped a few F-bombs,” a former diplomat told Reuters.

Growing Kurdish power has caused unrest among Christians in northern Iraq. The U.S. Commission on International Religious Freedom has said the Kurdistan government and Kurdish parties’ militias have subjected Christians to “pervasive discrimination and marginalization,” and advocates for those Christians say the Kurds have continuously encroached on their lands, which lie in disputed territory claimed by both the Kurdish region and Iraq.