Thomson won approval yesterday for its $17.6 billion takeover of Reuters from the British company’s editorial watchdog, but the deal now faces intense scrutiny from antitrust regulators and unions unhappy about expected job cuts.

The renamed Thomson-Reuters Corp. would reduce the number of major companies providing financial data, news, and trading systems to the financial services industry from three to just two and vault it slightly ahead of the current market leader, privately held Bloomberg LP.

The backing of trustees of the Reuters Founders Share company was a crucial first step in creating the world’s largest financial news provider. The trust, which controlled what is known as a “golden share,” was set up when Reuters listed on the London Stock Exchange in 1984 to safeguard the editorial independence of its journalism.

“We believe that the formation of Thomson-Reuters marks a watershed in the global information business,” a Swedish businessman and chairman of the trustee company, whose directors have the power to order any shareholder whose holding exceeds 15% to reduce their stake, Pehr Gyllenhammar, said.

The Thomson family of Canada, which will have a 53% majority stake, agreed to adopt the Reuters Trust Principles as long as it controls Thomson-Reuters, the companies said.

The chief executive of Reuters, Tom Glocer, 47, who will head the combined company, said that some “realignment” is likely to occur to meet a goal of $500 million in cost reductions over three years. But he played down the prospect of large-scale job cuts, pointing to the fact that Reuters has already made cost savings totaling around $1.8 billion over the past five years.

Reuters journalists, however, expressed their “deep concerns” in an open letter to Mr. Gyllenhammar, “over whether a reconstituted Reuters would maintain the high standards of journalism and the integrity, independence, and freedom from bias that have shaped the company’s 156-year-old reputation and are crucial to its future success.”

The management “just defended it really by saying that it’s good for business, it’s good for economies of scale,” a National Union of Journalists spokesman, Barry Fitzpatrick, said. “It’s all about cutting jobs, I would say.”

Investors fear that the deal could face a lengthy review by regulators has limited the advance of Reuters shares in London. While they rose 3.2% yesterday to 624.75 pence ($12.40), that’s still almost 10% below the current blended 690.5 cash and stock value of the deal.

“Antitrust authorities in Europe and the U.S. are almost certain to apply a more detailed and lengthy review of the acquisition than is typical, because of the limited number of companies that supply prices, data, news and financial tools,” an analyst at Credit Suisse in London, Simon Baker, said.

The combination of Reuters Group PLC, founded when Paul Julius Reuter began transmitting stock market quotations between London and Paris via the new Calais-Dover cable in 1851, and relative newcomer Thomson Corp. would generate sales in excess of $11 billion and just beat Bloomberg in terms of market share.

Reuters’s market share of 23% and Thomson’s 11% would combine for a total Thomson-Reuters Corp. share of 34%, according to April figures from Inside Market Data Reference. Bloomberg has a 33% share.

A Justice Department spokeswoman in Washington, Gina Talamona, said the acquisition is “something the Department of Justice’s antitrust division would be interested in looking at.”