NEW YORK ( TheStreet) -- Last year, Americans were sent about 84 billion pieces of junk mail, according to the U.S. Post Office, and they have apparently had enough.

Cities such as Chicago and Seattle have established "Do Not Mail" registries, similar to the popular "Do Not Call" initiative, to block companies form sending junk mail to consumers who sign up.

The campaigns are a big hit with consumers.

In fact, 81% of Americans "across all ideologies, age groups and income levels" support them, according to a study on privacy and advertising mail from the University of California, Berkeley, School of Law.

Frustration with mailboxes cluttered with fliers and catalogs has finally caught up with junk mail companies, and it's been a long time coming, study researchers say, as junk mail makes up about 50% of all mail delivered in the U.S. today.

"Our survey is in line with consumer polls conducted over the last four decades that reflect a frustration with advertising mail," says co-author Chris Hoofnagle, a Berkeley Law lecturer and director of information privacy programs at the law school.

"Americans may view advertising mail as a privacy issue because of database activities underlying the targeting of mail," says study co-author Jennifer M. Urban, assistant professor of law at Berkeley. "They also may dislike the sense of intrusion created when advertising material flows into the home."

Hoofnagle and Urban say one big obstacle to Do Not Mail initiatives is the U.S. Postal Service, which has lost "tens of billions of dollars" in recent years, and on average, loses $57 million per day, and as a result is "courting" direct marketing companies (the primary purveyors of junk mail) to send more mail.

"The USPS' fiscal challenges have created incentives for the agency that directly contravene recipients' desire to manage advertising mail," Urban says. "The Postal Service has created many innovations to help advertisers increase mail volume, but it's done little to assist Americans manage unwanted advertising mail."

To cut down on your volume of direct mail, contact the Direct Marketing Association and ask them to have your name removed from mailing lists. Write them directly at:

Mail Preference Service -- Direct Marketing Association, P.O. Box 643, Carmel, NY 10512-0643

Companies that with work within the DMA's guidelines will stop sending you junk mail for five years, at which point you'll need to re-register.

Also, avoid signing up for contests and coupons online or via snail mail -- it's a sure sign that you'll be added to that group's mailing lists.