(CNN) Senate Democratic leaders are joining forces with Republican Sen. Rand Paul of Kentucky to oppose a small portion of President Donald Trump's arms deal with Saudi Arabia.

Senate Minority Leader Chuck Schumer announced Monday he was supporting a resolution offered by Paul and Democratic Sens. Chris Murphy of Connecticut and Al Franken of Minnesota to block the sale of $510 million of precision-guided munitions to Saudi Arabia.

Paul and Murphy are expected to force a vote on their resolution -- which is possible under Senate rules for arms sales -- as early as Tuesday, according to Senate aides.

"I will support Senator Murphy's resolution of disapproval," Schumer said in a statement. "The human rights and humanitarian concerns have been well documented and are important: of equal concern to me is that the Saudi government continues to aid and abet terrorism via its relationship with Wahhabism and the funding of schools that spread extremist propaganda throughout the world."

Maryland Sen. Ben Cardin, the top Democrat on the Senate Foreign Relations Committee, came out against the munitions sale to Saudi Arabia last week, citing the Trump administration's decision to sell weapons to Saudi Arabia instead of trying to find a solution to the civil war in Yemen, where the Saudi-led coalition is accused of bombing civilians.

"I believe it's important for President Trump to present to us a strategy for how we're going to end the conflict in Yemen," Cardin told reporters on Monday.

With the backing of Schumer and Cardin, the vote on the Saudi arms sale could be razor-thin -- certainly much closer than the 71-27 vote to dismiss a similar resolution from Paul and Murphy last year.

Both Schumer and Cardin voted to dispose of that disapproval resolution, which was over a separate Saudi arms sale approved under the Obama administration.

But now Senate Democrats appear inclined to oppose the latest arms sale, as they have expressed concerns that the Trump administration is not pressing Saudi Arabia and others on human rights abuses.

Paul and Murphy say they're objecting to this arms sale because the precision-guided bombs are being used in the Yemeni civil war to target civilians.

"It's an arms race over there, and we're fueling it," Paul told CNN's Jake Tapper.

Paul told reporters Monday he thought the vote would be "very, very close" when asked about the whip count.

The $510 million munitions sale is part of the $110 billion arms agreement that Trump touted during his visit to Saudi Arabia last month.

The senators are able to object to that portion of the sale because it has been noticed by the State Department, where foreign military sales are subject to a 30-day congressional review period.

Most of the $110 billion Saudi sale has not yet reached that phase. Defense News reported last week that $85 billion of the deal is made up of potential sales that still need to be finalized.