According to the Wall Street Journal, Google and Yahoo are in talks with the Justice Department in an effort to head off an antitrust challenge to their proposed advertising agreement.

Although the settlement negotiations are at an early stage  investigators are continuing to build a lawsuit to block the deal, worried it would give Google too much power in online advertising.

In the settlement talks with the government, both companies have discussed concessions, including capping the volume of Google ads Yahoo would use, assurances that Yahoo would continue to compete in search ads, and a reporting mechanism to ensure compliance.

U.S. officials hope to impose measures that will ensure that prices advertisers must pay don’t rise significantly after the deal.

If the companies reach a settlement with regulators, its principles would likely be laid out in a consent decree that would be filed in court.

The companies recently agreed to delay implementing the deal until at least Oct. 22 to give federal and state antitrust officials time to complete their separate investigations.