The Department of Justice has started reviewing the practices of mobile carriers in the U.S., including AT&T (NYSE: T) and Verizon Wireless (NYSE: VZ), to determine if they have abused their power in recent years, reports the WSJ, which quotes unnamed people familiar with the situation.

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At this point, it’s unclear how big of a deal this is. The review is in its early stages and isn’t being considered an official inquiry, and no companies in particular are under investigation. However, the review likely piggy-backs on questions being asked by other lawmakers. The FCC has been exploring whether larger carriers are hurting smaller competitors by having long-standing exclusives on popular phones, like Apple’s iPhone. The Justice Department may also review whether carriers are “unduly restricting the types of services other companies can offer on their networks.”