Due to a suspicious substance, a Dallas Fire-Rescue hazardous materials response team was called to the Farmers Branch office of U.S. Senator John Cornyn.

Officials with the senator's office said the following Wednesday afternoon: "I can confirm that authorities have been called to our Dallas office to investigate a piece of mail. For more information, please contact Farmer's Branch PD."

The senator's office is on the 11th floor, which has been evacuated as a precaution, Farmer's Branch police said.

At 2:15 p.m., Dallas Fire-Rescue said all tests of the package to determine if it's hazardous came back negative. All other questions about the incident were referred to the U.S. Postal Inspector's Office.

DFR said two people were exposed to the package while checking the mail, but that no one was showing any signs of exposure to hazardous substances.

Sen. Cornyn's North Texas office is located at 5001 Spring Valley Road, ste 1125E. He has six other offices across the state and one in Washington D.C.

On Wednesday, the FBI is looking into letters sent to President Barack Obama and Sen. Roger Wicker, R-Miss. Both letters were postmarked Memphis, Tenn., and said, "To see a wrong and not expose it, is to become a silent partner to its continuance." Both are signed, "I am KC and I approve this message."

Reports of suspicious letters also came in from congressional offices in Michigan and Arizona, as police investigated the discovery of at least three questionable packages in Senate office buildings.

It is not yet known if the piece of mail being investigated at Cornyn's Dallas office is related to the other incidents.

