Shares of Compass Inc., an online real estate platform, dropped on Wednesday after a report that the New York Attorney General’s Office could be investigating the company’s dominance in New York City on antitrust grounds.

The Real Deal said agents with the Attorney General’s office have contacted some of New York City’s top brokerage firms asking for information about Compass International Holdings, which now ranks as the nation’s largest residential real estate brokerage.

Compass shares closed down 11.8% at $7.61 on Wednesday. The stock is down 28% this year, but up 23% over the past 12 months.

Compass could not immediately be reached. The New York Attorney General’s Office declined comment.

The Wall Street Journal reported on Jan. 9 that Justice Department antitrust enforcers wanted to investigate the $1.6 billion merger of Compass and Anywhere, the nation’s two biggest real-estate brokerages, but were overruled by senior officials, citing people familiar with the matter.

The acquisition closed after four months in January—far faster than the nine-month time frame the companies predicted it would take when they announced the merger in September—and led to the creation of Compass International Holdings.

The Journal, citing people familiar with the matter, reported that Gail Slater, the head of the Justice Department’s antitrust division, wanted to launch an extended review to determine if it was anticompetitive, but that Compass and its lawyers appealed to then-Deputy Attorney General Todd Blanche, who agreed that any concerns could be addressed without an investigation.

Compass also enlisted Mike Davis, a lawyer aligned with President Donald Trump, and known for helping to get conservative judges seated on the federal bench, to help argue its case to Blanche’s office, the Journal reported.

On Dec. 16, Senators Elizabeth Warren (D, Mass.) and Ron Wyden (D., Oregon) wrote a letter to the Justice Department’s Slater and Federal Trade Commission Chair Andrew Ferguson, urging them to “closely scrutinize” the Compass-Anywhere deal for potential violations of antitrust law. They warned that the transaction could “harm consumers by making it easier for these merged firms to keep commission fees artificially high and allow the merged company to exert greater control over the real estate market, consumer access, and the homebuying process.”

They said that the two companies “already command excessive market power in many markets,” including nearly 70% of residential sales by dollar volume in Northern California and more than 40% in New York City.

A spokeswoman for Blanche’s office told the Journal in January that the department “complied with its obligations” under antitrust law, adding that if the merger did occur, “nothing precludes the department from taking an enforcement action in the future if anticompetitive effects are found.”