The top Republican and Democrat on the Senate Foreign Relations Committee are squaring off over whether the committee should examine Secretary of State nominee Rex Tillerson’s tax returns as part of the confirmation process.

Tillerson, the chief executive officer of Exxon Mobil, is set to face the committee in January and, following tradition, will submit financial disclosure forms and ethics documents. But the committee’s ranking Democrat has also requested to see the nominee’s tax returns.

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“I think it is an important part of vetting this candidate because he has never made public disclosures of this type, as he has worked at ExxonMobil for his entire career and has never been in public service,” Sen. Benjamin L. Cardin, D-Md., wrote in a Thursday letter to the committee’s Democratic members. “Mr. Tillerson was actively engaged with many foreign governments that could become relevant if confirmed as Secretary of State.”

Cardin said Tillerson responded to a question concerning tax returns in the committee’s questionnaire by saying that he would provide the information. Cardin said he expects to receive Tillerson’s financial disclosure information by the end of the week, and he would contact Chairman Bob Corker, R-Tenn., about his request for the returns.

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Only three Senate committees can require nominees to provide tax returns. Though Foreign Relations isn’t part of that group, Senate Democrats have been pushing for all committees to have the authority, arguing that Trump’s wealthy nominees could have conflicts of interest. The Democrats also point out that Trump bucked decades of tradition by not releasing his own tax filings during the presidential campaign. 

Corker said in a statement that he was “deeply disappointed” that some of his Senate colleagues have implied the vetting process is not going as planned. 

“As is long-standing precedent for nominees considered by the Senate Foreign Relations Committee, the committee has not asked Mr. Tillerson to provide copies of his tax returns,” said Corker. “By all accounts, Mr. Tillerson is currently ahead of schedule in providing information to the committee.”

Corker noted Tillerson submitted his questionnaire three days after Trump announced his nomination. He said Tillerson will soon be submitting “extensive” financial disclosures and will go through the same FBI and ethics reviews as previous nominees. 

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”Our committee will carry out exactly the same procedures for Mr. Tillerson’s nomination that have been carried out since well before I joined the committee 10 years ago,” Corker said.

Corker had previously said Tillerson does not need to provide his returns. 

“Unless there was a case where there’s some irregularity that’s known, the committee just does not ask for tax returns,” Corker recently told The Washington Post. 

Asked if the Tillerson questionnaire will be made public, a committee aide responded, “In keeping with long-standing committee practice, the document is available to members of the committee and their designated staff.”

The committee has tentatively scheduled a two-part confirmation hearing for Tillerson on Jan. 11. But Cardin said he has discussed needing more time to vet Tillerson with Corker, and Corker told Cardin he would be open to adding another day of hearings. 

Tillerson’s ties to Russia have raised concerns among Democrats and some Republicans on the committee. If all Democrats oppose him, only one Republican “no” vote is needed for the committee to scuttle the nomination.

Rachel Oswald contributed to this report.

Contact Bowman at bridgetbowman@rollcall.com and follow her on Twitter @bridgetbhc.