The state-run Public Access to Court Electronic Records (Pacer) service deleted numerous court documents deemed incompatible with a software upgrade.
These included appeals heard by Justice Sonia Sotomayor prior to her appointment to the Supreme Court.
A famous racial discrimination case was among the expunged files.
Ricci v DeStefano, in which it was alleged that the race of Connecticut firefighters was taken into consideration when awarding promotions, was one of Justice Sotomayor's most notable cases during her time on the Court of Appeals.Barack Obama appointed Sonia Sotomayor to the Supreme Court in 2009
The lawsuit is one of several that have been permanently taken down by Pacer, which is tasked by the US judiciary with looking after the online archiving of court documents.
In an announcement two weeks ago, Pacer said the archaic "management systems" of the following five courts meant their files would no longer be available online.US Court of Appeals for the 2nd Circuit (New York, Connecticut, Vermont) US Court of Appeals for the 7th Circuit (Illinois, Indiana and Wisconsin) US Court of Appeals for the 11th Circuit (Georgia, Alabama, Florida) US Court of Appeals for the Federal Circuit (Washington DC) US Bankruptcy Court for the Central District of California
Justice Sotomayor served on the 2nd Circuit Court of Appeals from 1998 to 2009.
Hard copies will still be available from the courts in question, but for a fee of $30 (?18) - significantly higher than the $0.10 per page the service charges to access copies on the web.
Additionally, it can take days to receive non-digital records.A group of New Haven firefighters sued the city after it threw out test results due to race 'Fundamental' issue
Pacer has long faced criticism for its arcane structure, and for the fact that it charges for each record accessed.
Carl Malamud, the founder of non-profit Public.Resource.Org, and advocate of ensuring that government documents remain freely available online, told the BBC:
"It's ridiculous. An historical database is essential to the legal profession, and for that matter, to journalists or students."
"It's fundamental that justice is not done behind locked doors, but in public view," he added, citing the US Constitution's demand that legal records be made freely available.
"Today, public view is the internet."The Ricci case was an issue during Justice Sotomayor's confirmation hearings and later the Supreme Court
In conjunction with the Free Law Project and the Internet Archive, Mr Malamud has written to the five courts concerned, formally requesting the missing data.
"We would like to analyse the data for privacy breaches and we would like to provide public access to these important court records which have permanent historical value," the letters read.
The goal is to add the data to Recap, a service set up as an alternative to Pacer, and now jointly run by Princeton University and the Free Law Project.
Recap already has one million records in its archives.'Sky isn't falling' Two rulings involving gun control in Chicago and New York City are also no longer available
Lawyers and others who often interact with US courts have a separate system to access court records - one which is significantly more expensive, but nonetheless grants access to the same documents.
David Ziff, a lawyer who formerly worked in Seattle and New York City, says that the "sky isn't falling" as a result of Pacer's decision.
"Most of my annoyance is not that this is a terrible thing for many practitioners or professors - it's just that there just doesn't seem to be any reason for this," said Mr Ziff, who is currently a lecturer at the University of Washington School of Law.
Landmark cases missing
As well as Ricci v DeStefano, several important cases are now missing from Pacer.
These include:Center for Reproductive Law and Policy v. Bush (2002) - A case in which Judge Sotomayor upheld the Bush administration's position on not contributing funds to pro-choice organisations Pappas v Giuliani (2002) - A police officer appealed against his dismissal after posting racially offensive material to political groups Gant v Wallingford Board of Education (1999) - Judge Sotomayor ruled that a school had racially discriminated when it demoted a black child to kindergarten Hinrichs v Bosma (2005) - Judge David Hamilton, who was Barack Obama's first judicial nominee, determined that prayers in the Indiana House of Representatives must refrain from "using Christ's name or title or any other denominational appeal" National Rifle Association v City of Chicago (2009) - a unanimous court led by conservative judge Frank H. Easterbrook upheld Chicago's tough handgun law and cited a unanimous decision by the 2nd Circuit Court of Appeals (which included Justice Sotomayor) in Maloney v Cuomo (2009). Both records are now inaccessible
Mr Ziff noted that for students and others trying to better understand a court's ruling, being able to see the briefs that lawyers filed before a decision was made is incredibly useful.
The fact that Pacer charges a fee for that act makes the decision to remove access to certain files all the more perplexing.
"Where did all that money go - can't you use that money to store old [files] and make them available?" he said.