In protest of royalties fees which take effect next month, the amount of which has been recently estimated to surmount their revenues by nearly four times, America's largest and best-known streaming music sites, plus others worldwide, have gone silent for the day.

The sound of silence could grow familiar, some streamers are saying, if the US Copyright Royalty Board's recently imposed rate structure fails to be stayed by bills that are still before Congress.

This morning, Yahoo Music and LaunchCast, with the nation's second largest Internet radio audience, replaced all their music channels with links to SaveNetRadio.org, which represents the effort to stop the new performance royalty tier from being imposed. In a message on its music blog this morning, Yahoo Music's Ian C. Rogers states in unequivocal terms, his company will not continue to produce streaming music online if no legislative action is taken between now and July 15.

"The situation webcasters are in is simple: The new royalty rates are higher than the revenues anyone can hope to make from related advertising," Rogers writes. "In other words, we all lose money on Internet radio starting July 15th. Yahoo has no intention of operating LaunchCast radio as a loss-leader. This senseless rate hike needs to be changed, or our business will have to. And unfortunately the way we'd have to change our business would end up curtailing the great diversity that makes Internet radio uniquely compelling."

A similar, though shorter, message was to be found on the front page of Pandora, which recently had to shut off access to IP addresses outside the US anyway -- including from Canada -- in order to avoid an international royalties situation.

But the day-long stream-out was not a unanimous affair. At mid-morning, BetaNews was able to launch streams from AOL Music, with the nation's largest audience. (Curiously, our anti-spyware software stopped one attempt by a malicious control to take screen shots of us signing in to AOL Music with our screen name - which is something else AOL might like to know about.)

Also, London UK-based Last.fm -- which was recently purchased by CBS for $280 million -- opted out of today's protest, though it offered a long explanation with regards to why.

"We do not want to punish our listeners for our problems, period," writes Last.fm's Felix Miller. "If a commercial challenge comes up, we have to deal with it. We have always done that, as many people who have been using Last.fm for a while can attest to."

Miller goes on to state his company has been negotiating with royalties collection services in the UK and the US for what may be a more reasonable royalties rate, at least for his firm. "The only solution to this dilemma is commercial; make a commercial argument and see it through," Miller continues. What benefit does music have if no one is playing it anymore?"

Smaller streamers such as KOQX Blues Radio featured notices on their Web pages warning of dire consequences, though its stream was still audible this morning. Participation among terrestrial radio stations with Internet streams appears to be mixed, with many NPR stations' streams silent today.

Among non-NPR stations, the online stream for classical station KDFC in San Francisco played loud and clear, as did oldies station KOMA in Oklahoma City.

One of my personal e-mail addresses also received at least one item, automatically filtered into my spam pile, reminding me that if I can’t get my music fix from American stations, there’s at least one overseas channel where I could score.

Still, today’s silence is likely to be heard by several hundred thousand listeners, due in large part to the efforts of radio industry veteran and protest organizer Kurt Hanson. A complete list of participants - which includes not only Live365, MTV Radio, RealNetworks’ Rhapsody, and RadioIO, but also the news feed from Lincoln Financial Group – now appears on Hanson’s RAIN newsletter site.