Labor Sec. Tom Perez will formally declare his candidacy for the chairmanship of the Democratic National Committee on Thursday, according to a source familiar with his plans.

He'll do so on a conference call hosted by state party chairs supportive of his candidacy, the same source says. NBC News reported Tuesday that Perez planned to enter the race, which has so far been dominated by Minnesota Rep. Keith Ellison, this week.

The call for Democratic leaders, set to occur at 2:00 p.m., is hosted by 10 state party chairmen and two vice chairmen, including several from big states with large delegations to the DNC, which will select its next chairman in February. They include the chairmen of Texas, Pennsylvania, Virginia, Maryland and Nevada, along with vice chairmen from California and Ohio.

“As you may know, Tom Perez is considering running to be the party’s next DNC Chair. He is a proven leader, civil rights attorney, and has served in President Obama’s administration for the last 8 years where he has expanded opportunity for Americans across the country. Tom would like to have this informal discussion to hear from you on how we can make the party more inclusive and one that represents all Americans,” read the invitation to the call obtained by NBC News.

Perez, whose parents emigrated from the Dominican Republic, will also participate in a call with Latino leaders at 3:30 p.m., highlighting another potential source of support for him inside in the party.

Encouraged by the Obama White House and others, Perez has bided his time entering the race as he sussed out support among the roughly 450 members of the DNC and from other party leaders across the country.

Top Democrats uneasy with Ellison have been privately offering their support and encouragement to Perez, who has been closely following the leadership race while also considering a gubernatorial run in his home state of Maryland.

The pressure campaign may have worked. Perez has been working the phones aggressively in recent days is said to be eager to get his message out before politicking slows for the holidays. as Wednesday

Perez’ entry would set up a heavyweight bout between two progressives of color who each hail from different sides of the Democratic Party’s establishment-outsider divide. Ellison was a loyal Bernie Sanders supporter in the presidential primary, while Perez was a vocal Hillary Clinton backer.

But both are rare figures in that they are largely, though not universally, trusted and respected by both sides. After the primary, Clinton’s campaign worked with Ellison on ways to win over Sanders voters, while Perez was President Obama’s go-to ambassador to organized labor and progressive groups.

Perez earned a spot on Clinton's vice presidential shortlist, and was many progressives' favored option. Now, ironically, he may face off against some of those former boosters.

While it's unclear how much support President Obama will publicly offer, Perez, once he announces, will quickly emerge as Ellison's top challenger in a race that also includes New Hampshire Democratic Party Chair Ray Buckley and South Carolina Chair Jaime Harrison. The election is scheduled for late February, when members of the DNC will make their selection at a meeting in Atlanta.

After seeing other potential challengers drop out one by one, Ellison has built a large head start in the month since he announced his bid. The Minnesota congressman has the backing of progressive stalwarts like Sens. Elizabeth Warren and Bernie Sanders, Senate Minority Leader Sen. Chuck Schumer and civil rights hero Rep. John Lewis. He was also endorsed by the AFL-CIO.

But Ellison, who is Muslim-American, has faced questions and criticism about past comments on Israel and ties to Nation of Islam Leader Louis Farrakhan, which critics say is a distraction at best and disqualifying at worst.

And some in the party’s establishment are uneasy with handing the reigns of the party to a Sanders ally from one of the most liberal congressional districts in the country, worried he could divide the party or alienate the white working class voters the party needs to win back.

Among the roughly 450 members of the DNC who will actually vote for the next chairman, the race remains open. On a conference call Friday to brief Democrats on the status of their campaign, Ellison's team said they had secured at least 67 votes, according to a source familiar with the call. Though that number may have risen since, it suggests Ellison's support on the committee may be less commanding than his overwhelming endorsement lead might suggest.

And Perez boosters are undaunted by Ellison's endorsements, noting that while there are some Democrats who feel Ellison is unacceptable, Perez could be a consensus pick.

They doubt that, for instance, Warren or Schumer or AFL-CIO President Richard Trumka will object to Perez’s chairmanship, even if they publicly declared their support Ellison. Meanwhile, one of the DNC’s largest donors, Israeli-American billionaire Haim Saban, has said Ellison would be a “disaster” for the party while the Anti-Defamation League has raised concerns as well.

Jewish Ellison supporters dismiss the criticism as a smear campaign, noting Ellison distanced himself from youthful comments long ago and that their reemergence has not stopped new supporters from joining his team.

And supporters say Perez, the son of Dominican immigrants from Buffalo, can speak to both Hispanics and white working class voters, while his work with the Civil Rights Division of the Justice Department earned plaudits from African American leaders.

Still, Perez will face criticism from some on the left for his support for the Trans-Pacific Partnership trade deal and other Obama priorities he was sent out to sell to liberals. Moreover, many Sanders-aligned voters will likely view Perez’ candidacy as yet another attempt by the party's establishment to marginalize them and keep them from power.

Others who have been advocating a more technocratic DNC chair may object to the fact that Perez has virtually no experience with electoral politics, having won only one election to municipal government. Instead, he's spent much of his career in the federal government, which has different politics from those of the Senate and House races.