WASHINGTON – An annoyance at best and a costly scam at worst, robocalls have tied up American phone lines for decades.

And as the technology behind the calls has evolved, so have the efforts to block them — but some say that proposed new regulations are chasing after the wrong culprits.

Robocalls today look quite different from those 15 or 20 years ago. In the days of traditional copper-wire telephone service, auto-dialing calls and covering up caller ID information was expensive and complicated — meaning those calls often were the work of large companies, rather than individual scammers. Placing calls overseas was especially costly.

Now, however, anyone with a laptop and an Internet connection can make robocalls from anywhere in the world at very little cost.

The Do Not Call registry was established by the Federal Trade Commission in 2004, and more than 220 million Americans have added their phone number to the list in the years since. The registry has largely been effective at stopping more traditional robocalls — those made by American telemarketers and companies that want to avoid the fines that come with ignoring the rules.

But the registry doesn't offer much protection against individual robocallers overseas, meaning that many Americans who put their number on it still receive unwanted calls.

In the past, telephone providers have argued that they don't have the legal jurisdiction to block calls in stricter ways. Now, Congress and the Federal Communications Commission are trying to ensure that legal protection exists.

The FCC is scheduled to vote next week on a proposal to codify telephone providers' legal ability to block calls themselves and offer call-blocking technology to customers. Sen. Claire McCaskill, D-Mo., is set to introduce a bill this week that would expand the authority of the FCC and the FTC even further. The bill would allow the commissions to track down people who are robocalling from outside the United States. It also would strengthen the penalties and fines for those who are caught.

McCaskill will speak at a hearing Wednesday before the Senate Special Committee on Aging, where she is the top Democrat. Senior citizens are often seen as being particularly likely to fall for robocalls, and it's not uncommon for third parties to sell lists of seniors' numbers to scammers.

But there has been pushback from researchers and pollsters, who say that existing regulations already impede their ability to do what they consider legitimate work.

The phone offers a random sample and a wide net that can't be matched by other strategies, and the proposed regulations would hurt that, said Howard Fienberg, director of government affairs for the Marketing Research Association.

"The phone is still generally considered the closest you can get to a full picture of the country," he said.

McCaskill acknowledges that strengthening federal enforcement powers alone would not be enough to stop robocalls. Private telephone companies will have to play a role as well, she said.