Web giants Facebook, Google, Twitter and Skype have banded together to oppose an online social networking privacy bill in California that would require users’ permission to display personal information such as home addresses and phone numbers.

The bill, introduced last February by state Senate Majority Leader Ellen M. Corbett (D-San Leandro), started out as legislation aimed at minors to create stronger privacy safeguards for their personal information.

Corbett said in an interview that Facebook and other companies argued that the focus on youth would encourage lying about age. She said the Silicon Valley networking giant protested that youth wanted to better control their information.

“But I felt strongly that certain personally identifying information shouldn’t be available too easily. I wasn’t saying that it couldn’t be provided but that address and financial information should be only given with permission,” Corbett said in a telephone interview. “So we amended the bill to focus on all users.”

That has the titans of Silicon Valley’s Web industry up in arms. In a letter to Corbett earlier this week, Facebook and other popular sites protested the proposed legislation.

They told Corbett that they oppose the bill because it “would significantly undermine the ability of Californians to make informed and meaningful choices about use of their personal data, and unconstitutionally interfere with the right to free speech enshrined in the California and United States Constitutions.”

They added that their firms, including Skype, Twitter, Zynga, Yahoo and eHarmony are important engines of economic growth for the state.

But their responsibility to follow such laws would create “significant damage to California’s vibrant Internet commerce industry at a time when the state can least afford it.”

The bill would also allow parents to request any personal identifying information about their children under the age of 18 be removed within 48 hours of asking. Violations of the bill would result in fines of up to $10,000 for each violation.

The bill has passed a senate committee and would have to gain a majority of votes in the full senate before going to the full legislature. If passed, it would go to the governor’s office for approval.

Observers said Web giants are afraid of the bill passing because it could set a legal precedent for other states and federal lawmakers. U.S. federal lawmakers have introduced several privacy bills but analysts say turning any one of those bills into law this year will be difficult.

In her bill, Corbett said that the Polly Klaas Foundation found that 42 percent of online teens say they post information about themselves on the internet so others can contact them. More than half the respondents say they have been asked personal questions online.

Facebook sets 13 as the minimum age for users. But Consumer Reports last week found that an estimated 7.5 million Facebook U.S. users are under 13, with about 5 million of those users under 10, according to their survey of more than 3,000 homes.

The social network giant has lamented the difficulty of verifying age on the Web site. It said once it identifies underage users, it kicks those users off the site. But it thinks the better approach is to educate children about safety and privacy rather than keep them offline.

“Recent reports have highlighted just how difficult it is to implement age restrictions on the Internet and that there is no single solution to ensuring younger children don’t circumvent a system or lie about their age,” said Facebook spokesman Andrew Noyes in a statement. “We appreciate the attention that these reports and other experts are giving this matter and believe this will provide an opportunity for parents, teachers, safety advocates and Internet services to focus on this area, with the ultimate goal of keeping young people of all ages safe online.”

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