By RICHARD ESPOSITO
April 30, 2012

Envelopes containing suspicious powder were sent through the mail to at least seven locations in Manhattan, primarily Wells Fargo banks, in an apparent May Day protest, 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."

Four of the seven samples have tested negative so far. The envelopes apparently contained corn starch.

Police believe the suspicious envelopes were mailed by militants from within the Occupy Wall Street movement.

Labor, immigration and Occupy Wall Street activists are planning protests for "May Day," May 1, which also is known as international workers' day. The intent is to show the "1 percent" what life without the working class' "99 percent" would be like.

San Francisco-based Wells Fargo may have been singled out for the 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, intended for May Day delivery, arrived at the banks early.

"They underestimated the efficiency of the U.S. Postal Service," one official said.

Occupy Wall Street threatens to block New York-area tunnels and bridges in the morning in an effort to keep commuters from arriving at work, police officials said. They also have urged pickets at "99 locations," an obviously symbolic number.

The Occupy movement has identified 30 to 40 locations, including banks, where they intend to block entrances, officials said.

There will be a significant amount of police officers on duty to counter the protests, though police officials did not give specific numbers on the planned deployment. The day shift is the largest of three tours, with a minimum of 7,000 officers routinely on duty and the ability to hold the overnight shift for coverage.

An additional large number of officers will be on duty for a labor march slated for 5:30 p.m. That march has for several years been a peaceful event by organized labor.

In Los Angeles, officials said 2,500 police will be on duty for the May Day events, and there will be a command center with nearly 100 officers.

ABC News' Michael S. James contributed to this report.
http://abcnews.go.com/US/day-protest...4#.T59RP-2wVea