Washington ? The Supreme Court on Monday let stand a lower-court ruling affirming the national do-not-call list’s constitutionality.

Without comment, the justices rejected an appeal by telemarketers who argued that the popular anti-telemarketing registry imposed unconstitutional limits on their rights to free speech.

In the year since it took effect, more than 64 million telephone numbers have been posted to the list, according to the Federal Trade Commission, which is in charge of enforcing the list. Telemarketers risk a fine of up to $11,000 for each number they call on the list.

More than 500,000 complaints have been filed with the FTC against more than 130,000 companies said to have made telemarketing calls to numbers on the list. About 200 companies are repeated offenders with 100 or more complaints each.

Despite these complaints, surveys show the list is working. In one study done last summer by the Customer Care Alliance, 87 percent of consumers who registered said they received fewer phone calls; these consumers received an average 30 sales calls in a month before the list was put into effect. Now they are receiving six.

So far, the FTC and the Federal Communications Commission, which also polices the do-not-call list, have brought only a handful of actions against telemarketers.