SACRAMENTO, Calif. (AP) – The Internal Revenue Service has moved to seize 23 properties, including vacation homes in Lake Tahoe and Maui, as part of an investigation into fraudulent billing practices against a casino-operating Indian tribe in Northern California, according to court documents made public Wednesday.

Federal court documents filed late Tuesday say a developer, the administrator of the United Auburn Indian Community and a tribal quality-control contractor conspired to bilk the tribe out of more than $18 million by inflating bills. No criminal charges have been filed.

The bills were related to a construction project that included new headquarters for the tribe, which operates the Thunder Valley casino in Lincoln, a suburb of Sacramento.

The civil forfeiture complaints allege the building contractor paid more than $7 million in kickbacks to the tribe's quality control contractor. The government says the quality control employee used part of the money to buy tribal administrator Gregory Baker a Lake Tahoe vacation home and an in-ground pool at his home in Newcastle, 30 miles northeast of Sacramento.

Baker's attorney, Tom Johnson, denied wrongdoing by his client and emphasized that no criminal charges have been filed in the case.

“It's just a civil lawsuit. Like any other civil lawsuits, people can say a lot of things that simply aren't true,” he said. “They've been investigating for several years, and there's no criminal indictment.”

Lauren Horwood, a spokeswoman for the U.S. Attorney's Office, said federal prosecutors are continuing their investigation.

Tribal spokesman Doug Elmets said Baker was placed on leave Wednesday, and the contract with the quality-control expert, Darrell Hinz, ended several years ago. Hinz's attorney, William Portanova, also noted that no criminal charges had been filed against his client.

“Just because the numbers are big, doesn't necessarily mean that there's something illegal,” he said.

Federal prosecutors say the 23 properties were acquired illegally with money from the kickbacks. They also moved to seize other assets, including bank accounts, stock shares and a 2010 Mercedes-Benz.

Any assets seized by the government should be returned to the tribe if obtained through fraud, Elmets said.

The complaint says the tribe originally signed contracts worth more than $16.5 million with Bart Volen of Lincoln to complete the building project at its administration offices in Auburn. But it says the tribe wound up paying nearly $42.7 million for the work, much of which went for inflated change orders.

Volen's attorney, Matt Jacobs, said he could not comment because he hadn't read the government's court filings.

Baker approved the change orders, according to an affidavit filed by IRS special agent Daniel M. Norman. Johnson, Baker's attorney, said the tribe “was very, very happy with it. They were happy with the amount of money they paid; they were very happy with the result.”

He said the tribe and Thunder Valley have flourished in the eight years since Baker became administrator, growing into one of California's most profitable casinos.

Volen subcontracted the work to another firm, which is not implicated in the complaints.

The subcontractor sent Volen change orders worth $6 million, but the government says Volen submitted $24 million in inflated invoices to the tribe for payment. Of about 180 change orders he submitted between late 2006 and early 2008, the government says about 169 included overcharges.

For instance, the subcontractor billed $40,217 for paving work, but the tribe paid $1.9 million, according to the government filings.

The IRS affidavit alleged that at other times, Volen or his associates simply changed amounts in the subcontractors' invoices by adding or changing digits from hundreds of dollars to thousands.