MarketWatch.com has tied up with B2B giant Thomson Financial, a unit of Thomson Corp, to develop a customized news service branded Thomson ONE.

Financial analysts from Thomson and journalists from MarketWatch.com will collaborate to develop news and information for Thomson ONE customers, the companies said.

MKTW’s Own Coverage: The deal will allow MarketWatch to expand its staff of 80 journalists by as much as 50 percent and provide Thomson with news coverage on financial markets in North America, Asia and Europe.

The deal throws the two companies into direct competition with Reuters, Bloomberg and Dow Jones for the high-margin institutional audience. Reuters said it finds “this move surprising,” a spokeswoman in London said.

WSJ Online (sub. req.): Phil Lynch, CEO of Reuters America, said in an interview that Reuters had told Thomson Financial late last year that it was concerned Thomson was marketing Thomson’s product for financial advisers to insititutional clients as well. That move put it in direct competition with Reuters.