The company, which owns the rights to the 2013 movie, is seeking compensation from people who pirated the movie.
But the Federal Court of Australia said the company had to pay a large bond before it could access their data.
Many Australians regularly illegally download digital content, such as movies.
Dallas Buyers Club LLC (DBC) said it had identified 4,726 unique IP addresses from which the film was shared online using BitTorrent, a peer-to-peer file sharing network.
But the Federal Court of Australia said DBC would have to pay A$600,000 ($442,000; Â£283,000) to obtain customer details.
In a judgement published on Friday, the court also limited any damages DBC could seek from alleged copyright infringers.
The ruling will prevent the company from so-called speculative invoicing.
This is where account holders accused of piracy are threatened with court cases that could result in large damages unless smaller settlement fees are paid.
In April, the court had ordered internet service providers (ISPs) to give DBC details of customers accused of illegally downloading the movie.
But in May, that order was put on hold, as the court told DBC to show it a copy of the letters it wanted to send to customers.
Friday's judgement said that even after the court had seen the proposed letters, as well as the scripts DBC staff would follow in phone conversations with alleged infringers, it was unclear how much money the company would ask customers to pay.
The judgement said DBC wanted to pursue alleged infringers for:
Justice Nye Perram said the second and third requests were "untenable".
Having seen what DBC proposed to demand under the clauses, and the "potential revenue it might make if it breached its undertaking to the Court not to demand such sums, it seems to me that I should set the bond at a level which will ensure that it will not be profitable for it to do so," he said.
An Australian court has blocked a US company from accessing details of customers who illegally downloaded the US movie Dallas Buyers Club.