By Sarah E. Needleman and Jeff Horwitz

Facebook Inc. said it would assist the company behind popular videogame "Fortnite" in its high-profile legal battle with Apple Inc., as the social-media giant ramps up its own counterattack against what it says are the iPhone maker's self-serving measures cloaked in the interest of privacy.

Facebook has been feuding with Apple for months on issues ranging from prices for paid apps to privacy rule changes.

As part of a pledge to assist challenges to what it called Apple's anticompetitive behavior, Facebook plans to provide supporting materials and documents to Epic Games Inc. The "Fortnite" parent sued Apple earlier this year, claiming the tech giant's App Store operates like a monopoly. Facebook said it isn't joining the lawsuit but helping with discovery as the case heads to trial next year.

A spokeswoman for Epic declined to comment.

In a blog post Wednesday Facebook also sharpened its criticism of Apple's plan to enable users to restrict certain apps from collecting personal data, saying those policies could imperil small businesses while potentially benefiting its own bottom line.

"This is not really about privacy for them," said Dan Levy, Facebook's head of ad products. "This is about an attack on personalized ads and the consequences it's going to have on small-business owners."

An Apple spokesperson didn't immediately respond to a request for comment.

Apple has said starting early next year its iOS 14 operating system will give iPhone and iPad users the option to no longer share personal information that many developers rely on to tailor ads. When users open an app, they will see a message asking permission to track what other apps and websites they visit, their location and other behaviors.

Apple's plan has drawn criticism from a range of businesses and trade groups. They include the publisher of DMG Media, operator of the Daily Mail and MailOnline, and the Partnership for Responsible Addressable Media, a coalition of advertisers and ad-tech companies that was formed in July in an attempt to forestall Apple's change. A group of trade associations filed a complaint with France's competition authority in October, saying that Apple's plan was anticompetitive.

Facebook itself is facing challenges to its business practices. The Federal Trade Commission and 46 states sued the company earlier this month, accusing it of buying upstart rivals to choke off competition. The FTC's case aims to force Facebook to unwind acquisitions of WhatsApp and Instagram, two of its landmark deals. Facebook countered that the FTC had previously approved those acquisitions and said that people and small-businesses choose to use its free services and advertising because of the value that it provides them.

By aiding Epic, Facebook is wading further into a battle over Apple's App Store commission that is being waged by several other companies, including Spotify Technology SA and Tinder owner Match Group Inc.

Epic filed suit against Apple and Alphabet Inc.'s Google in August after the companies pulled "Fortnite" from their app stores because the developer added an unauthorized payment system to the survival game that skirted a 30% fee they both collect on in-app purchases. Apple countersued a month later, accusing Epic of duplicity and greed.

Apple and Google have said the commission they charge is in line with what most other app marketplaces charge and helps cover the cost of store services they provide, such as user privacy and security.

In August Facebook said Apple's commission was hurting small businesses that had started charging for special events and experiences through their mobile apps to make up for financial losses caused by the pandemic. Apple a month later said it would give businesses a reprieve from paying the fee on such in-app sales until the end of the year.

More recently Apple said it would halve the commission it charges smaller developers that sell software through its App Store. The iPhone maker said last month that starting next year it will collect 15%, rather than 30%, of App Store sales from companies that generate less than $1 million in revenue through the software platform, including in-app purchases.

Write to Sarah E. Needleman at sarah.needleman@wsj.com and Jeff Horwitz at Jeff.Horwitz@wsj.com

(END) Dow Jones Newswires

12-16-20 1330ET