Thursday’s decision by the Federal Communications Commission to encourage mobile carriers to auto-block robocalls might help mitigate the barrage of telemarketers and scammers calling consumers, but advocates warn that consumers should be critical as to how ー and which ー calls are blocked, as well as to whether they’ll ultimately pay the cost of the new service.

Many consumers were previously able to opt into these services ー though not necessarily aware that they could. Now phone companies can make the weeding out of suspected robocallers a default setting and instead let the customer opt out of the service.

“The FCC is not requiring them to use blocking by default. They’re saying you can without violating the law,” Gigi Sohn, a fellow at the Georgetown Institute for Technology Law and Policy, told Cheddar. “If you do block calls by default, you have to tell the customer, and give the customer the option to opt out.”

In the United States, there were nearly 4.7 billion robocalls dialed in May, according to YouMail, a free call-blocking app. That brings the total number of robocalls dialed in the country for this year to nearly 25 billion overall.

More at Cheddar.