A settlement reached this week threatens to strike a blow to an established standard of residential real estate: the 6 percent sales commission. It also will change who pays it. The deal, reached after a yearslong court battle initially brought by a group of home sellers in Missouri, calls for the powerful National Association of Realtors, which has long regulated the way U.S. homes are sold, to amend its rules on how Realtors for sellers and buyers are compensated.

In most real estate transactions in the United States, both the seller and buyer have an agent representing them. For decades, there’s been a standard for paying these agents: a commission of between 5 and 6 percent of the home’s sale price, covered by the seller and split between the two agents.