(RNN) - A letter addressed to New York Mayor Michael Bloomberg has tested positive for ricin, according to the New York Times.
A second letter was sent to a building in Washington that houses Mayors Against Illegal Guns, a group co-founded by Bloomberg.
Bloomberg never received the letter addressed to him, which arrived Friday. The Washington letter was opened on Sunday.
The two letters were postmarked Shreveport, LA.
Shreveport Mayor Cedric Glover confirmed the city is working with the FBI and the Joint Terrorism Task Force to apprehend those responsible.
"We are also taking the necessary steps to protect local USPS & Government Plaza personnel as well as local citizens from any possible harm," he tweeted.
According to the American Postal Workers Union, New York and Washington employees were notified of the letters and told officials have no reason to be any employees would be at risk from handling them as they passed through the mail system. The APWU reports employees were told the substance was not in a form that could be inhaled or readily ingested. The union was notified by the post office about the letters.
It's the second ricin scare in recent months.
In April, letters containing ricin were sent to President Barack Obama and Sen. Roger Wicker, R-MS.
James Everett Dutschke, 41, of Tupelo, MS, was arrested for possession and use of a biological agent as a weapon for allegedly sending the letters.
Ricin is highly toxic and can be deadly in even small doses.
Copyright 2013 Raycom News Network. All rights reserved.