Republicans lawmakers have added to a funding bill a provision meant to help speed up the passage of a waiver to allow retired Gen. Jim Mattis to serve as secretary of defense.

The move is aimed at short-circuiting Democratic objections to one of President-elect Donald Trump's key Cabinet picks. Congress must pass the funding bill by midnight Friday or else face a government shutdown.

Mattis retired after more than four decades in the Marines in 2013, and thus needs Congress to grant him a waiver from a World War II-era law that bars ex-military members from the top post at the Pentagon within seven years of retiring from the service, an effort to preserve the principle of civilian control of the U.S. military. Congress has done so just once, for George Marshall in 1950, stipulating that "no additional appointments of military men to that office shall be approved."

Democrats, already concerned about a Cabinet shaping up to be heavy on military brass, are considering how to respond to the maneuver.

"The American people are entitled to regular order and thoughtful scrutiny of nominees and any potential waivers," House Minority Leader Nancy Pelosi said in a statement Tuesday. "Brushing aside the law that enshrines civilian control of the military – without discussion, in a massive must-pass funding bill – would set a terrible precedent."

At least six Democrats must join with Republicans in order to pass the spending bill, which has a standard 60-vote threshold to avoid a filibuster.

Democratic lawmakers have expressed annoyance that the bill, which must be brought to the floor in a matter of hours in order to ensure it can be passed by the Friday deadline, remains shrouded in secrecy.

"Remember 'read the bill?' Rs are not even allowing us to read the legislation that will fund the government come Friday," Sen. Claire McCaskill, D-Mo., griped on Twitter. "Regular order? BS."

"Ridiculous that we're sitting around guessing what's in the bill to fund the entire government that they want us to vote on in less than three days," she said .

Still, it's unlikely Democrats will risk pushing the government into a shutdown over the Mattis language, which will not complete the waiver process, merely expedite it come January.

Late Tuesday, Republicans added additional language that would preserve the 60-vote threshold for the waiver, an addition that Minority Whip Dick Durbin, D-Ill., called "an improvement."

In addition to Mattis, who was formally nominated Tuesday, Trump has also named retired three-star Army Gen. Michael Flynn to be his national security adviser. On Wednesday, Trump picked retired Marine Gen. John Kelly for secretary of Homeland Security. He is reportedly considering retired Adm. Mike Rogers, currently the head of the National Security Agency, to be his director of national intelligence and at least two former flag officers, Gen. David Petraeus and Adm. James Stavridis, among the contenders to be secretary of state.

Mattis is popular on both sides of the aisle and many Democrats have said they think he is a strong choice to lead the Pentagon and would have a positive influence on Trump .