"Competition on the merits can raise rivals' costs," he added, "but that says nothing about anticompetitive effects."

However, Microsoft must then prove an actual technological benefit that outweighs this anticompetitive effect.

Attorneys general of several states, including New York, also said they would sue to block the merger, citing its potential anticompetitive effects.

The spokesman also noted that any transaction would have "significant anticompetitive effects."

In neither case did the Supreme Court find those justifications sufficient if anticompetitive effects were proved.

The Commission has also looked closely at the potential anticompetitive effects of vertical integration.

"I will require hard evidence before I make a decision not to challenge a merger that otherwise looks like it could have anticompetitive effects."

And the firm also pours cold water on Sprint's specific claims about the merger's anticompetitive effects.

One issue is the effect of 'ease of entry' in the post-merger situation, where there are potential anticompetitive effects.

The Guidelines also spell out in some detail what anticompetitive effects the Department is concerned about.