White House press secretary Jen Psaki said Tuesday that the White House has engaged with 375 lawmakers and their offices in a push to have Biden's $1.9 trillion COVID-19 relief bill passed.

"In the past two weeks alone, we've engaged with over 375 members and offices, over 100 of which were bipartisan engagements, and our COVID team has also started biweekly bipartisan member briefing  with the Senate and House where, of course, we talk about the American Rescue Plan and the impact it can have," Psaki said.

Psaki added that Biden met with nine Democratic senators virtually on Monday and will meet with the Senate Democratic caucus virtually on Tuesday.

White House press secretary Jen Psaki discussed the partnership between longtime competitors Merck and Johnson & Johnson to ramp up production of the single-shot J&J vaccine, which was greenlighted by the Food and Drug Administration Saturday.

"The two largest health care and pharmaceutical companies, Merck and Johnson & Johnson, usually competitors, are coming together to expand production of the vaccine, Johnson & Johnson’s vaccine drug substance, as well as increase its fill finish capacity," Psaki said. "They will enter into a historic manufacturing partnership to expand that, I should say."

Psaki touted the White House's role in getting the companies to work together, saying it "speaks to the ability of this administration, broadly, to bring them to the table and work together to address the pandemic in the country." She also discussed how the federal government is working to facilitate making the vaccine available, including providing support from the Department of Defense and using the Defense Production Act.

"The US Government will facilitate this partnership in several key ways including invoking the Defense Production Act to equip two Merck facilities to the standards necessary, safely manufacture the vaccine, and asking the Department of Defense to provide daily logistical support to strengthen Johnson & Johnson's efforts," Psaki said.

Sen. Joe Manchin, D-W.V., has said he wants to see some changes to Biden's COVID-19 relief package, including it becoming more targeted, a phrase heard Monday after moderate Democrats met with Biden.

Manchin, who is a key swing vote in the split Senate, told reporters on Capitol Hill that he takes issue with the provision that adds $400 per month to unemployment insurance, saying he feels like people are coming off of unemployment now, so increasing it "doesn't make sense."

"It's kind of hard to explain...I would prefer that they stay at $300 [per month]," Manchin said.

Democratic leadership says since this is not a position supported by the majority it will be a tough needle to thread. It is the last minute for Manchin to be seeking the kind of change that would really shake up the bill. The goal is to have the Senate's reconciliation bill ready to hit the floor late Wednesday.

-ABC News' Trish Turner

In floor remarks Tuesday, Senate Majority Leader Chuck Schumer affirmed that the COVID-19 budget bill could come to the Senate floor "as early as tomorrow" and continued to advocate for a robust rescue package.

"The American Rescue Plan is designed to finish the job. That's what the American people sent us here to do that's what our government is for," Schumer said. "Not to sit back and wait for problems to fix themselves, not to cross our fingers and hope the economy will fix itself on its own."

Minority Leader Mitch McConnell, meanwhile, continued railing against the bill, accusing Democrats, as he has for weeks, of loading the bill with "liberal wish list" items. He said the Democratic plan would stall the economy rather than energize it.

"It's more like a plan to keep it shut down," McConnell said. "Mostly it's just what democrats promised almost a year ago, taking advantage of the crisis to check off unrelated liberal policies."

-ABC News' Allison Pecorin