SEATTLE, Wash. — Attorneys general in Washington and four other states filed an antitrust lawsuit Wednesday, accusing real estate giants Zillow and Redfin of illegally colluding to dominate the online ...

The legislation comes amid a heated debate among major real estate players over private listings. The dispute is especially fraught in Washington, where private listings are already rare.

In the last year, Zillow has rigorously defended its ban on homes not listed on MLS — a rule the company has now adjusted to fit its own venture.

Washington State, with its dynamic economy, diverse population, and thriving technology sector, has long been an attractive destination for real estate investors. Home to global giants like Amazon, ...