But for a few exceptions such as Facebook’s Messenger app, Uber doesn’t allow third-party apps to display its ride prices and wait times next to those of competing services. Lyft has an identical prohibition.

Because of these rules, developers of apps that pull data from both Uber and Lyft have found their access cut off. In turn, other app makers have avoided even attempting to use Uber’s and Lyft’s data feed tools.

But one pair of app developers has decided to give it a shot, and on Tuesday released Ride Fair, a mobile app that lets people in the U.S. request rides from both Uber and Lyft. Its main goal is to let users compare how quickly they can get a car from the two services and whether “surge” pricing—a price hike during busy times—is in effect.

“Surge pricing doesn’t mean you don’t have options,” Phillip Wall, one of Ride Fair’s makers, told Fortune in explaining his inspiration for building the app with fellow developer Steve Blackwell.

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When riders open Ride Fair, the app determines their location and shows them a list of nearby Uber and Lyft cars along with the estimated time it would take to be picked up. Users who select a particular ride—presumably the faster or cheaper one—are taken to the corresponding ride-hailing app to book it.

Until now, Uber and Lyft haven’t been fans of such apps. In 2013, a San Francisco startup, Corral Rides, built an app that let users compare prices and availability of Uber, Lyft, and Sidecar rides, as well as Muni—San Francisco’s public transportation system. However, within a couple of months, Lyft requested that Corral remove its data from the app, according to TechCrunch. Corral also removed some information about Uber rides at Uber’s request. At the time, neither Uber or Lyft had a public data feed available—Corral had scraped that information from their services without authorization. (Ironically, Lyft eventually acquired the team behind Corral, after it shifted to building its own ride-hailing service.)

More recently, Uber asked Boston-based UrbanHail to stop using its data tools, or API, because it violated Uber’s terms of use. While Lyft has identical restrictions, the company did not contact UrbanHail—most likely because Uber did so first, making it unnecessary for Lyft to get involved.

While most developers seem to have accepted Uber and Lyft’s rules when it comes to their APIs, not everyone is convinced that they are in the best interest of consumers. Harvard assistant professor Ben Edelman has even raised questions about whether the restrictive policies, described by Uber as its right to establish, are legal under antitrust laws.

The restriction, he said, “is calculated and intended to block competition—a purpose considered improper under competition laws, and a special stretch for Uber in light of the company’s positions on related issues of competition and regulation.” Via email, Edelman added that while both companies have similar policies, Uber’s dominant position in many markets gives it more power to squash competition through such policies than Lyft.

Maurice Stucke, of the Konkurrenz Group, told Fortune that this Uber’s approach can be especially problematic if its policy’s purpose is to protect the company’s monopoly or help it become one. “The greater the risk that the price transparency would let consumers find the better price, the greater the anti-trust risk,” said Stucke.

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The one defense the ride-hailing companies could have—and seem to lean on—is that allowing certain use of their APIs would somehow harm or degrade their service or app, said Stucke. For example, they could argue that the process of accessing their data overloads their servers or makes their apps slower.

In response to questions about its policy, Uber turned to its usual justification that it wants to wants to control how its service is displayed to users outside of its own apps.

“We have an API with a few guardrails in order to preserve the integrity of the Uber experience for users across all apps,” an Uber spokesperson told Fortune about the company’s restrictions on use of its API.

Reached for comment about the company’s policy, a Lyft spokesperson said that “if a developer is identified as violating our Terms of Service, we work collaboratively with our developer community to ensure that they be given time to remediate.”

Both Uber and Lyft claim that because they work with third-party apps like Google Maps, Messenger, and Citymapper as partners, they’re able to have more control over how their services and brands are used. However, it’s still unclear why they’re concerned that smaller third-party developers wouldn’t be able to abide by such guidelines.

Recognizing that Uber and Lyft could cut them off at any time, Wall, from Ride Fair, is hopeful. He says that the benefit users get from his app could help convince the companies that allow such apps. “I hope there will be a dialog among consumers,” says Wall, who doesn’t plan to turn Ride Fair into a business or ever charge for the app. “I really just don’t think it’s fair.”

An earlier version incorrectly stated that Ride Fair is only available in San Francisco. The story has been updated.