(CNN) -- Frustrated Republicans are retaliating for a Democratic play to weaken their hand in opposing presidential nominations, forcing an all-night session into Thursday's early hours.
Votes on judicial and other appointments took place early Thursday morning, part of the fallout after the Democratic majority enforced a rule change to expedite consideration of appointments, the so-called nuclear option.
Until last month, longstanding Senate rules required a supermajority of 60 votes to break a filibuster over a presidential nominee. Republicans fiercely opposed the change, which now allows the majority Democrats to break filibusters with 51 votes.
Democrats, who hold a 55-45 advantage in the Senate, said Republicans had abused the filibuster privilege around President Barack Obama's nominations, and the only way for him to staff his second-term administration promptly and move stalled judicial appointments was to speed things up through a rules change.
"The Obama administration and its allies have done just about everything to get what they want, one way or the other -- even fundamentally altering the contours of our democracy when they couldn't get their way playing by the rules," Senate Minority Leader Mitch McConnell said in floor remarks Wednesday. "We saw the culmination of that with the majority leader's power grab in the Senate last month."
Republicans are requiring the marathon session if Democrats want to clear a long list of nominees before leaving for vacation next week.
GOP escalation of the rules fight renewed attention to sharp partisan wrangling one day after lawmakers trumpeted a compromise House-Senate budget proposal brokered across party lines.
The first vote in the extended session came shortly after 1 a.m. ET as the Senate approved 51-44 Nina Pillard's nomination on the federal appeals court in Washington. For some, the appointment has been a steppingstone to the Supreme Court.
The Senate will continue plowing through the backlog of nominees later Thursday. Senators will vote on the confirmation of Chai Rachel Feldblum to the Equal Employment Opportunity Commission.
Senate Democrats began enforcing the "nuclear option" this week, stoking Republican ire.
All-nighters could continue for days. Democratic leaders said they were prepared to stay in session virtually around the clock through Saturday night to confirm a list of 10 nominees to a variety of senior posts.
They range from lesser-known appointments -- such as Patricia Wald to the Privacy and Civil Liberties Oversight Board -- to critical positions -- such as Jeh Johnson to be homeland security secretary.
There are also several federal district court judge appointments on the list as well as nominees to Pentagon posts and the State Department.
Customarily, Senate leaders work together so the chamber can conduct its business during more regular hours. But because of strict parliamentary rules, it's easy for just one senator to hold things up.
In this case, the whole GOP conference is upset.
So why are they working overnights?
According to Senate rules, a certain number of hours of debate can still be demanded by any senator once a filibuster is broken.
Known as "post-cloture debate time" in Senate parlance, up to eight hours of debate time is allowed for nine of the 10 nominees on Majority Leader Harry Reid's list. For Johnson, the homeland security nominee, debate can last for 30 hours.
Typically, Senate leaders would agree to allow that debate time to run with the Senate out of session. But Republicans are angry about the changes to the filibuster rules and are requiring the Senate to stay in session.
Reid accused Republicans of obstructionism.
"It is hard to imagine a more pointless exercise than spending an entire day waiting for a vote whose outcome we already know," Reid said about the Pillard nomination. "But Republicans insist on wasting time simply for the sake of wasting time. It's no wonder Americans overwhelmingly support the changes Democrats made to the rules last month in order to make the Senate work again."