A team of FBI and IRS agents on Tuesday searched a North Dallas office building, authorities said.

An FBI spokeswoman said agents were at 13155 Noel Road "conducting law enforcement activity," but she declined further comment. Lisa Slimak, spokeswoman for the U.S. attorney’s office in Dallas, said she could not confirm or deny the existence of an investigation.

Brint Ryan, who has an office in the building, said about 40 agents were at the offices of Garza & Harris.

Joe B. Garza is a Dallas tax planning attorney known for his “aggressive” tax shelters.

Garza could not be reached for comment. His office phones were not taking messages on Tuesday.

Garza's website says he has negotiated and closed "more than $300 million of debt transactions" and "over $1 billion of tax exempt bond transactions as bond counsel for the state of Texas."

“His tax advisory work is a fundamental component of his practice, serving over 2,000 clients nationally and internationally,” the website says.

But Garza’s promotion of certain shelters has resulted in costly adverse tax rulings against his clients, according to court records.

Garza promoted and sold to clients a variety of the notorious "Son of Boss" tax shelter, which the IRS ruled was abusive if used to create artificial tax losses that could offset other income, according to federal court records.

U.S. Tax Court Judge Mark V. Holmes in Washington, D.C., said in a 2015 ruling in one case that Garza testified to having sold more than a dozen of the transactions to different clients. Garza provided his clients with opinion letters that said the tax plans would "more likely than not" withstand IRS scrutiny, tax court records show.

“Garza, however, relied on certain ‘facts’ to reach his ‘more likely than not’ conclusion, and these ‘facts’ were just plain wrong,” Holmes wrote.

Holmes noted that Garza engaged in “sometimes quite aggressive tax planning.”

Staff writers Steve Thompson and Karen Robinson-Jacobs contributed to this report.