Envelopes containing suspicious powder were sent through the mail to at least seven locations in Manhattan, primarily Wells Fargo banks, police officials said.
"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."
Several samples tested negative -- evidently containing 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.
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 NYPD was making a false assumption.
Police had no suspects in the mailings, the AP reported.
Labor, immigration and Occupy Wall Street activists were planning public protests for "May Day," May 1, which also is known as international workers' day.
The police believed San Francisco-based Wells Fargo 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,'" New York police spokesman Deputy Commissioner Paul Browne told ABC News.
The envelopes, believed intended for May Day delivery, evidently arrived at the banks early, according to police.
"They underestimated the efficiency of the U.S. Postal Service," one official said.
ABC News' Michael S. James and Bill Ritter contributed to this report.