NEW YORK — NBC is requiring people who want to view online video streams of certain Olympics events to first prove that they subscribe to a cable or satellite television system.

Users who click on certain videos on the NBC Olympics site are asked to identify their providers and prompted to provide a username and password for their cable or satellite account. If they don't have a password, they must enter their account number. The registration is one-time only.

The policy guarantees that no one will be able to bypass cable and satellite systems to watch Olympic events. The risk for NBC Universal is irritating their customers, many of whom probably don't carry their cable account numbers with them.

"At least some people will think it's an intrusion they don't need," said Lee Rainie, director of the Pew Research Center's Internet and American Life Project.

NBC Universal, which has said it expects to lose more than $200 million on the Vancouver Games, said the satellite and cable providers required the registration in return for helping to defray some of the cost of Olympics rights.

The rule affects live streaming and replays of events and competitions, such as Friday's opening ceremony, which was not posted online until after it aired on NBC in all U.S. time zones. People who wanted to see skier Lindsey Vonn's news conference earlier this week about her injured shin also needed their account numbers handy.

It did not affect highlight packages of certain events, which are shown with no such registration, said Gary Zenkel, president of NBC Olympics. That tends to be what most online visitors are most interested in seeing, he said.

Zenkel said NBC doesn't have any evidence that the rule is a turnoff for Web site visitors, although he will be monitoring.

"We have spent nearly two years working with the cable operators to streamline this," he said.

NBC Universal has deals with cable and satellite providers covering 96 percent of the country, he said. At least one system, Cablevision, acknowledges the policy may be an inconvenience. That provider said its customers who subscribe to cable and the Internet will be able to bypass the registration, although that doesn't start until Monday.

People were required to identify their cable or satellite provider on NBC's Olympics Web site in 2008, but not asked to verify with their account numbers. Back in the relative infancy of online offerings, in 2004, NBC required its users to give a Visa credit card number, even though they weren't charged.