The International Brotherhood of Teamsters could issue its long-awaited presidential endorsement as soon as Wednesday, union spokesperson Kara Deniz confirmed to CNBC on Monday following a meeting members held with Vice President Kamala Harris in Washington.

"We don't just represent registered Democrats. We represent registered Republicans and independents," Teamsters President Sean O'Brien said in a press conference after the meeting. "So we have to take [it] into consideration and she recognized the diversity of our membership as it relates to political affiliation."

With 50 days until the November election, the Teamsters, which has 1.3 million members, is one of the last organized labor groups that has yet to issue a presidential endorsement.

Traditionally, the Teamsters have endorsed the Democratic presidential candidate, but only after both parties hold their nominating conventions.

This year, however, O'Brien made it clear that the union would wait to endorse the candidate who, he said, presented the best option for working families — even if that meant bucking decades of tradition.

On Monday, Harris made her pitch for the union's endorsement in the meeting with rank-and-file Teamsters, along with O'Brien and other members of the union's executive leadership.

"The Vice President appreciates the opportunity to meet with IBT leadership and discuss how she has worked for her entire career to support and defend unions, including as part of the most pro-union administration ever," a Harris campaign spokesperson said in a statement to CNBC on Sunday.

The meeting came as both Harris and her opponent, Republican former President Donald Trump, court working-class voters.

"Vice President Harris cast the deciding vote for the Butch Lewis Act, which saved over a million pensions — and as president, she will work hand-in-hand with Congress to pass the PRO Act," the spokesperson added.

Both Trump and President Joe Biden have joined similar Teamsters roundtables since the group began hosting them in December.

"You don't hire someone unless you give them an interview," O'Brien said on CBS' "Face the Nation" earlier this month.

Throughout this vetting process, with O'Brien at the helm, the Teamsters have engaged more actively with the Republican ticket more than the union has historically done.

O'Brien raised eyebrows, for example, when he spoke at the Republican National Convention in July, becoming the first Teamster ever to speak at the GOP nominating event.

But the Teamsters president also condemned Trump's comments later in the summer, where the Republican applauded the idea of firing workers who threaten to strike.

"Firing workers for organizing, striking, and exercising their rights as Americans is economic terrorism," O'Brien said in response to those comments.