Bernie Sanders notched his first Senate endorsement Wednesday, while Hillary Clinton will be gaining the support of one of New York's largest immigrants rights group just days ahead of the state's primary contest.

Democratic Sen. Jeff Merkley of Oregon wrote an editorial in Wednesday's New York Times explaining his choice in backing Sanders, praising his Vermont colleague for "boldly and fiercely addressing" the country's biggest challenges.

The Oregon senator commended Sanders' opposition to trade deals, his stance against fossil fuels and pushes towards renewable energy, and his staunch advocacy of campaign finance reform.

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"[H]is leadership on these issues and his willingness to fearlessly stand up to the powers that be have galvanized a grass-roots movement," Merkley wrote. "People know that we don't just need better policies, we need a wholesale rethinking of how our economy and our politics work, and for whom they work."

Merkley strayed away from any criticism of Sanders' rival and current Democratic front-runner Hillary Clinton, however, even complimenting Clinton for her "lifelong" track record.

"From her time advocating for children as a young lawyer to her work as first lady of Arkansas and the United States, and as a senator and secretary of state, Hillary Clinton has a remarkable record," he said. "She would be a strong and capable president."

The New York transit union also threw its weight behind Sanders Wednesday, providing the Vermont senator with a much coveted union boost.

Members of the Transport Workers Union Local 100, which represents about 42,000 New York City public transportation workers, stood behind the senator as he announced the union's endorsement at the Brooklyn Historical Society.

"Together, we are going to end these disastrous trade agreements that have cost us millions of good-paying jobs and, by the way, have led towards a race to the bottom," Sanders said Wednesday morning. He touted unions as the "last line of defense against a vicious corporate agenda" responsible for bringing economic collapse to America and promised to advance legislation that would make it easier for workers to join unions.

The campaign of Democratic front-runner Hillary Clinton also announced an important endorsement ahead of New York's April 19 nominating contest.

The former New York senator earned the support of the the New York State Immigration Action Fund Wednesday at a roundtable meeting with officials from the group.

The endorsement comes just as Clinton pledged to create a new national Office of Immigrant Affairs that would help ensure immigrants and refugees are able to fully integrate into their communities. The office would facilitate programs at the federal, state, and local levels and lead efforts in coordinating integration policies.

At the roundtable in Manhattan, Clinton committed to $15 million in grants for that effort.

CBS News Digital Journalist Hannah Fraser-Chanpong contributed to this report.