Apple subpoenaed Valve in November as part of its ongoing litigation with Fortnite developer Epic Games, and it’s demanding that Valve provide extensive sales data for more than 400 games, according to a new filing (via PC Gamer).

The move comes amid Apple’s ongoing fight over Epic’s efforts to avoid paying iOS App Store fees. Apple argues that Valve’s data is necessary to calculate the size of the market of Epic’s “available distribution channels,” as Epic could theoretically offer its games through Steam in addition to other digital marketplaces. But the data is also immensely valuable in assessing the marketplace for games and apps — a space in which Apple’s iOS App Store continues to compete with Valve’s Steam marketplace.

Valve contends that Apple’s demands are extraordinary and is contesting the order.

In one request, Apple calls on Valve to procure documents that show the company’s:

(a) total yearly sales of apps and in-app products; (b) annual advertising revenues from Steam; (c) annual sales of external products attributable to Steam; (d) annual revenues from Steam; and (e) annual earnings (whether gross or net) from Steam.

Apple argues that this data is “crucial” to help it determine “the total size of the market for Epic’s available digital distribution channels.” The courts have already asked Samsung to provide “almost identical” information, Apple said in the filing.

In addition, Apple also demands that Valve procure documents that show:

(a) the name of each App on Steam; (b) the date range when the App was available on Steam; and (c) the price of the App and any in-app product available on Steam

Valve argues that the requests are overly broad. According to Valve’s position statement in the filing, “Apple gave Valve a list of 436 video games it says are available on the Epic Game Store and Steam, and (a) demanded Valve identify, from 2015 to the present, every version and all digital content or items for each of these games on Steam, then (b) provide exhaustive information about all of them.”

The requested information includes dates on sale, price changes, gross revenues for “game version and item, broken down individually,” and Valve’s revenues “related to these versions, content and items.”

Valve argues these demands would “impose an extraordinary burden on Valve to query, process and combine a massive amount of to create the documents Apple seeks” and that it does not keep this data as part of the “ordinary course of business.” (The filing also notes that Apple had reduced its request for data from “all 30,000+ games on Steam over ten years” to “436 games over six years.”)

Valve also argues that “much of what Apple seeks is sales and pricing information for third party games,” but that the company is taking a “shortcut” by subpoenaing Valve instead of getting the information directly from third-party developers.

On Wednesday, Epic filed a formal antitrust complaint against Apple with the European Commission, arguing that Apple has “not just harmed but completely eliminated competition in app distribution and payment processes.”