LinkedIn (NYSE: LNKD), the leading professional social networking site, lost as much as 6 percent of its value Monday on a report that Facebook (Nasdaq: FB), the No. 1 social networking site, will start direct competition.

Rather than just mount a social networking and games service, Facebook will launch a professional job board, akin to what LinkedIn already offers, Dow Jones Newswires reported. Facebook gained as much as 2  percent in value, increasing the company's market capitalization to $68.78 billion.

LinkedIn's value, though, dipped to $10.64 billion as its shares fell $5.88 to $102.98.

Both companies are based in Mountain View, Calif.

Analyst Doug Anmuth of JPMorgan Chase (NYSE: JPM), one of the co-underwriters of Facebook's IPO, kept his target price of $135 for LinkedIn because the challenge is not a material threat to LinkedIn. His target price for Facebook is $45.

Facebook representatives declined comment.