May 1, 2012— -- Letters containing suspicious white powder arrived in the mail rooms of Manhattan banks as well as City Hall and News Corp. today as a series of May Day protests unfolded around the city.
Labor, immigration and Occupy Wall Street activists spearheaded the protests. May 1 is known as international workers' day.
At least seven locations in New York City, primarily Wells Fargo branches, received menacing letters containing the white powder on Monday and today.
"This is a reminder that you are not in control," said a message that arrived with the envelopes. "Just in case you needed some incentive to stop working we have a little surprise for you. Think fast you have seconds."
The letter ended with a taunt.
"F--- THE BOSSES F--- THE BANKS F--- THE PIGS 'Happy May Day.'"
Several samples tested negative. The envelopes evidently contained corn starch, police said. Later, all the powder samples were determined to be non-toxic, The Associated Press reported.
The receipt of the white powder prompted evacuations at bank branches, police told the AP, but caused no injuries.
One of the mailings was addressed to Mayor Michael Bloomberg, but it never made it to City Hall. It was opened instead in the mail room of a nearby building on -- ironicallly -- Gold Street, where the mail is screened.
Two suspicious letters were also found today in the basement of the New Corp. headquarters at 1211 Avenue of the Americas, at the Wall Street Journal and Citicorp headquarters.
Police initially suggested the suspicious envelopes could have been mailed by militants from within the Occupy Wall Street movement, but a spokesman for Occupy Wall Street denied any connection to the mailings, saying the police were making a false assumption.
The police believed San Francisco-based Wells Fargo bank might have been targeted for white powder mailings because about half of a key dozen Occupy Wall Street members have backgrounds in Oakland, San Francisco and Berkeley, and similar incidents occurred in California earlier this week, police sources said.
In the New York cases, the envelopes mainly appear to have reached low-level workers at the bank branches.
"Apparently, the message was aimed at the mail room workers among the '99 percent,'" Deputy Police Commissioner Paul Browne told ABC News.
Some of the envelopes, believed intended for May Day delivery, arrived at the banks early, according to police.
"They underestimated the efficiency of the U.S. Postal Service," one official said.
ABC News' Alyssa Newcomb contributed to this report.