Congress in the United States has approved legislation intended to stop the flow of unwanted e-mails, or spam.
Critics say the bill will lead to more spam messages
US Senators adopted the "Can-Spam Act" following a vote by the House of Representatives on Saturday.
The measures - including fines and jail terms for offenders - are seen as vital in the US, from where most spam comes.
But activists warn the legislation does not go far enough and could even make matters worse by approving spam that follows key guidelines.
The legislation brings in penalties for individuals and companies that send out junk e-mails to recipients who have said they wish to unsubscribe.
But the BBC's David Bamford, in Washington, says it will not stop mass e-mail sendings entirely.
Nor will it prevent pornographic messages being sent out, though the law does state that pornography must be clearly labelled as such.
Anti-spam campaigners, who have been demanding legislation, are very unhappy with the new law, our correspondent adds.
They wanted spamming to made completely illegal, and what they have got, they say, is a law that tells 23 million US businesses they are now free to send mass e-mails as long as they follow certain rules.
But New York Senator Charles Schumer, one of the chief backers of the bill, said: "There's no single solution to solving the spam scourge, but this bill takes a number of needed steps to help people reclaim their inboxes."
The authorities are working with the internet service providers
"With this bill, Congress is saying that if you're a spammer,
you could wind up in the slammer," he added.
The bill now goes to President George W Bush for signing and the new law is expected to come into effect in January.
In the meantime, the authorities are working with the main Internet service providers to improve technology that tracks down those responsible for unsolicited pornography or fraudulent services that are often in themselves illegal.
But they face a tough challenge, our correspondent says.
This is not only because of court rulings arguing legitimate freedom of expression, but also with pornographers who use technology that hides their points of origin.