(CNN) As the Democratic primary candidates aggressively campaign for labor support, the Teamsters on Friday rolled out the details of their newly expanded endorsement process, including recently taped interviews with Sens. Bernie Sanders and Elizabeth Warren .

The International Brotherhood of Teamsters, which represents 1.4 million workers, is among the largest in the country. Over the last month or so, nearly a dozen candidates have sat down on-camera to make their cases to union voters. Nine hopefuls, including former Vice President Joe Biden, have signed a pledge promising their support on issues Teamsters members recently voted to prioritize ahead of the primary.

"I think the candidates are trying to resonate and talk about what issues are important to working people more than what they did last time (in 2016)," Teamsters General President James P. Hoffa said in an interview. "And I think they're doing a good job."

Hillary Clinton finished nine percentage points ahead of President Donald Trump (51% to 42%) with union households in 2016. Democrats will hope that margin widens come 2020. Warren, Biden and Sanders have all actively sought labor support and appeared on picket lines with striking United Automobile Workers members. Sanders in particular has made labor a focal point of his campaign, and been a fixture alongside workers protesting for higher wages and a union.

To be eligible for the Teamsters' official backing, candidates -- including Trump -- must agree to a three-point pledge assuring their support for labor-friendly trade deals, federal efforts to enhance and protect collective bargaining rights, and legislative action to protect endangered pension funding. Union members can track the process on a new website launched late Thursday. The candidates are also being asked to promise official neutrality should their staffs, as a number have already done, move to unionize.

The Teamsters also announced plans to hold a candidate forum on December 7 in Iowa.

When the union chose Clinton over Trump in 2016, the announcement came in late August. Hoffa didn't specify when a choice would be made this time around, suggesting it might not come until, or after, the Democratic National Convention next summer in Milwaukee, Wisconsin. The process, which is meant to more deeply engage candidates and rank-and-file union members, will culminate with Hoffa delivering a recommendation -- based in part on a survey of local leaders -- to the general executive board.

Hoffa pointed to the fluid nature of the crowded race, and the increased attention on labor issues, as reasons the Teamsters might take their time in picking a horse. So far, most major unions have been slower to jump behind a single candidate.

"This is changing so fast. You know, who would have imagined that Bernie would have a heart attack, who would imagined the controversy with regard to Biden and his son," Hoffa said. "Those are unknown things. And there's always unknown things that happen in campaigns, especially when you have a long time like this."

There are, however, already a number of clear divides among the candidates publicly vying for Teamster support. Most notable is their backing -- or opposition -- to "Medicare for All" single-payer health care, the signature proposal of Sanders' campaign. A number of labor leaders and some vocal union members have expressed concern over a move to Medicare for All.

Hoffa is among the skeptics.

"The Teamsters have health care for all. And I just think we have to educate (the candidates) on that issue. I can't believe they would say that we're going to give up our insurance," he said. "That's something we would be very, very strong on. That's just not something that we would concede."

Still, he spoke warmly of his and the union's relationship with all of the leading candidates -- and the efforts of union members to engage them on the trail. According to the union, Teamsters have made more than 100 contacts with candidates over the last three months, asking them 95 questions. Twenty Teamsters locals in 14 states, with a focus on the early-voting hubs, have taken active roles. Midwestern swing states like Ohio, Wisconsin, Michigan, and Pennsylvania will also see a burst of door-knocking, phone calls, text messaging and other digital outreach.

"I'm very heartened because I happen to know all these candidates. One way or another, over the years, we got to talk -- when Biden was vice president, Warren in the Senate. Bernie we've known for years and (New Jersey Sen. Cory) Booker we've known forever," Hoffa said. "And all these people come together with a lot of experience and it's a very talented group of people."