A bill moving through Congress designed to clarify rules for advertising via fax machines could expose consumers to a flood of unwanted solicitations, according to consumer groups and activists battling against junk faxes.

In late July, the Junk Fax Prevention Act was passed by the full House and the Senate Commerce Committee, and it is awaiting a Senate floor vote. The bill mirrors current law by banning unsolicited faxes, but makes explicit an exception for companies that have "established business relationships" with consumers or other businesses.

Under that exception, consumers who once purchased a product, or even sought information, from a company could be sent faxed promotions even if they had expressed no interest in future transactions or had not provided their fax number. The relationship could be at least five years old, but no more than seven, under the bill's terms.

Several business groups sought the language to make it clear that the limits on faxes were not intended to bar routine commercial dealings or prevent stores from alerting longtime customers of sales and other offers. But opponents said the exception is too broad and potentially allows people to fax more than they do now.

"This should be called the Junk Fax Promotion Act, not prevention act," said Robert Biggerstaff, a retired computer engineer in South Carolina who has sued fax marketers and administers a Web site that documents all U.S. court cases on the topic.

Biggerstaff estimates that 2 billion faxes are sent every year, and that the legislation could allow for twice that number.

Technology has enabled a proliferation of junk faxes, because computers can be harnessed to send faxes by randomly dialing area phone numbers without incurring long-distance charges. This has led to the growth of companies providing "blast fax" services.

In a nightmare scenario envisioned by consumer advocates, a popular national retailer could decide to send out fax blasts to hundreds of thousands of randomly dialed numbers, or to lists of fax numbers purchased from marketing firms.

Because so many people shop at this retailer, the blast faxes would reach many people with whom the giant retailer could claim an existing relationship, said Lawrence M. Markey Jr., staff attorney for the Foundation for Taxpayer and Consumer Rights.

Proponents of the legislation say it would give consumers new protection by requiring fax marketers to offer recipients the opportunity to remove themselves from any future messages. Failure to honor that request could result in fines and civil damages.

"The House bill requires junk faxes to include, on the first page, a clear and conspicuous notice to consumers that they have the right not to receive future junk faxes from the sender," said Rep. Edward J. Markey (D-Mass), one of the chief sponsors of the bill, along with Rep. Fred Upton (R-Mich.).

Business groups supporting the bill say blast faxes are used most by unscrupulous companies or scammers that won't abide by any laws. Legitimate firms, they say, honor opt-out requests and need to be able to freely fax clients and other firms with whom they regularly do business.

That's not good enough for Kenneth Koury, a Southern California lawyer who early this year bought his 12-year-old daughter a fax machine because she and her friends frequently fax each other joint school projects or information about homework assignments.

"Within a few weeks, all these faxes start coming in on her phone line," Koury said. His daughter's fax number "is unpublished, unlisted and had never been used."

Koury said many of the faxes, touting everything from travel and mortgage deals to stock tips, come in the middle of the night. Even if the ringer on the fax machine is turned off, Koury said, the machines makes enough noise to disturb his daughter's sleep.

Bill Adler, a Washington author whose elderly parents are frequently awakened by faxes coming in the middle of the night, said he that worries many fax marketers will stretch the definition of existing business relationship and won't honor requests to opt out of future faxes.

The bill was sought by a wide variety of businesses in response to new rules issued last year by the Federal Communications Commission.

Shortly after Congress passed the original junk-fax legislation in 1991, the FCC announced that faxes could be sent to existing customers, even though the law did not include that exception.

In the more than 10 years since then, numerous state courts have ruled that the exception is invalid and rejected efforts by fax marketers to use it as a defense in lawsuits against them. But state judges cannot compel federal agencies to change their orders.

The 1991 law "acts as a ban on fax advertisements unless the recipient has given 'prior express invitation or permission' to receive the fax," K. Dane Snowden, head of the FCC's bureau of consumer and government affairs, told a congressional hearing in June.

After watching a proliferation of junk faxing and complaints from small businesses and consumers, Snowden testified that the agency "concluded that an established business relationship would no longer be sufficient to constitute the necessary permission under the [law] to allow the lawful transmission of an advertisement to a person's fax machine."

So the agency issued federal rules requiring fax marketers to have prior permission in writing.

Business groups, including real estate agents, insurance companies, newspaper publishers and wholesalers, objected, saying that requiring written permission would impose a crushing burden on firms that rely on faxes to do business beyond advertising.

"If someone contacted a Realtor and said there's a house, could you fax me the listing sheet, we'd have to get written permission," said Marcia Salkin, senior policy representative for the National Association of Realtors.

The organization estimated that for all real estate transactions that were completed in 2003, 67 million fax-permission forms would have been required.

As a result of the outcry, the FCC suspended the new rules until January, pending another review.

But the marketing and other industries went to Congress, preferring a new law.

"What the FCC did was like killing a fly with a jackhammer," said Jade West, senior vice president for government relations of the National Association of Wholesaler-Distributors, who led a coalition of industries supporting the bill. "We tried very hard to get a balance."

Consumer advocates agree that the FCC's new rules went too far. But they do not want an opt-out system, in which marketers to have the ability to fax even one unsolicited advertisement just because a consumer once did business with that firm.

Instead, some urge a system whereby permission is considered granted when the recipient has provided his or her fax number or has granted oral approval.