Biden released a video on Twitter Sunday night throwing his full support behind efforts for unions to organize, mentioning an effort by employees in Alabama, but not specifically mentioning Amazon, which is currently trying to campaign against workers’ efforts there.

"You should all remember, the National Labor Relations Act didn't just say that unions are allowed to exist. It said that we should encourage unions. So let me be really clear: It's not up to me to decide whether anyone should join a union. But let me be even more clear: It's not up to an employer to decide that either. The choice to join a union is up to the workers," Biden said. "Full stop."

Biden goes on to say "no supervisor should confront employees about their union preferences" and that every worker should have a "free and fair choice to join a union."

"It's your right. Not that of an employer. It's your right," Biden said. "No employer can take that right away."

His video message is being met with praise from Sen. Bernie Sanders, I-Vt., who tweeted this morning thanking the president for his message.

"If Amazon workers in Alabama – a strong anti-union state – vote to form a union, it'll be a shot heard around the world. If they can negotiate higher wages & better working conditions in the South, it'll benefit every worker in America," Sanders said in the tweet.

-ABC News' Justin Gomez

Rep. Ro Khanna, D-Calif., and 22 other House progressives have sent a letter to Biden and Harris urging them to overrule the Senate parliamentarian and keep the $15 minimum wage in the $1.9 trillion COVID-19 relief package.

"We must act now to prevent tens of millions of hardworking Americans from being underpaid any longer," the letter said. "You have the authority to deliver a raise for millions of Americans."

Biden and his chief of staff Ron Klain have said they don’t want to overrule the top procedural official in the chamber. Additionally, they don’t have the votes to do so given that Sens. Joe Manchin, D-W.Va. and Kyrsten Sinema, D-Ariz., have said they oppose eliminating the legislative filibuster and Manchin also opposes the $15 minimum wage measure pushed by the House.

-ABC News' Benjamin Siegel

Sens. Bernie Sanders, I-Vt., and Ron Wyden, D-Ore., are dropping a planned amendment to penalize corporations that don’t pay at least $15 per hour in an effort to raise the minimum wage for as many people as possible after the Senate parliamentarian ruled a straight wage increase out of bounds under reconciliation, two Democratic sources confirmed to ABC News.

One source close to Sanders said that he is determined to pass a wage increase and is "looking at all available strategies" to get it done. One of the sources told ABC that the progressives', "plan B is on hold."

"We worked through the weekend, and it became clear that finalizing ‘Plan B’ with the caucus would delay passage and risk going over the jobless benefits cliff," the source said.

There were many questions about how the Wyden-Sanders amendment would work, some of the questions coming from Democrats. Sen. Mark Warner, D-Va., expressed concern Sunday that corporations might move jobs overseas in reaction to the penalty. Some economists questioned how the amendment would work with corporations that have franchises.

The $15 minimum wage increase has been a foundational issue for progressives in the new Congress.

-ABC News' Trish Turner

Biden travels from Wilmington, Delaware, where he spent the night, to the White House Monday morning. In the afternoon, the president meets virtually with Mexican President Andrés Manuel López Obrador.

Biden will broach a variety of topics in his discussion with López Obrador including managing increasing migration flows, combating cross-border narcotics trafficking and addressing the ongoing health crisis, according to a senior administration official. This will be a follow up to the conversation between the two leaders on Jan. 22.

Included in the discussion of migration flow will likely be the reluctance in the Mexican state of Tamaulipas to accept families with young children. An administration official confirmed to ABC News that Mexican officials had rejected families with children under the age of 6, and as a result, they were then released into the interior of the U.S. The official described it as "creating a challenge" for the U.S. in managing migration flows.

The senior official underscored that the Trump-era protocols used to expel nearly everyone attempting to cross the border, known as Title 42, are a temporary measures employed while immigration authorities work to build capacity for migrant processing in the U.S.

Broadly, the two leaders are expected to discuss avenues for continued cooperation and partnership on security, trade and migration.

The White House COVID-19 response team holds a briefing at 11 a.m. and White House press secretary Jen Psaki holds a briefing at 12 p.m.

-ABC News' Quinn Owen