(AP) — Hundreds of federal and local law enforcement agents have seized roughly 100 Northern California houses purchased with money wired to the United States by a Chinese-based crime organization and used to grow massive amounts of marijuana illegally, authorities said Wednesday.

The raids culminate a monthslong investigation focusing on dozens of Chinese nationals who bought homes in seven counties. Most of the buyers were in the country legally and came from as far away as Georgia, Illinois New York, Ohio and Pennsylvania, U.S. Attorney McGregor Scott said.

Much of the pot was shipped back to those states through Atlanta, Chicago and New York City. The drug is legal in California but requires permits to grow and is still illegal under federal law.

“This criminal organization has put a tremendous amount of equity into these homes through these wire transfers coming in from China and elsewhere,” Scott said in an interview with The Associated Press. “We’re going to take it. We’re going to take the house. We’re going to take the equity.”

None of the buyers was arrested as authorities seized the houses in what the U.S. Department of Justice called one of the largest residential forfeiture operations ever. Prosecutors will now ask judges to transfer ownership of the properties to the U.S. government.

Authorities were trying to learn if the buyers were brought to the United States for the purpose of buying the houses and were indebted to the criminal organization.

Down payments were financed by money wired from China, authorities said. The buyers generally used the same Sacramento real estate agents, borrowed from private lenders instead of traditional banks, and used straw buyers who purchased the properties on behalf of the real owners.

The federal crackdown on the illegal pot operations comes as California is months into creating the world’s largest legal marijuana market amid uncertainty about whether the U.S. government will try to shut it down.

More than 500 officers, including SWAT teams, fanned out over two days to search and seize about 75 houses and two real estate businesses. The remaining 25 houses were raided previously.

Black-market pot farms have been a widespread problem in Northern California for at least a dozen years. Suburban tract homes are transformed with high intensity lights and irrigation pipes, gutted to add ventilation pipes and air filtration systems to vent the tell-tale smell through the attic, and stacked with tables full of marijuana plants that could produce multiple crops each year.

Investigators have said the growing systems alone cost tens of thousands of dollars.

Authorities often are alerted when the houses catch fire because of illegal electrical hookups or when they are found to be using extraordinary amounts of electricity to power the equipment.