The commission blocked the takeover because the acquisition would have resulted in Emap controlling 70% of the market for the supply of construction project information and contact data.
With little in the way of realistic alternatives, customers could have faced price rises and a reduction in choice.
Emap, through its subsidiary Glenigan, and ABI are by far the largest providers of this kind of data to the construction industry, which uses the data to win new business.
Diana Guy, chairman of the Competition Commission inquiry group, said: "It is likely that the merged company would have even more scope to do so and reduce innovation and quality improvements."
She added that the other providers of data in the sector have very small market shares in comparison and did not provide a realistic alternative for customers, saying: "The merger would therefore remove the choice for customers".
The deal, which was negotiated over the summer, would have seen media giant Emap take over ABI's subscription and information bulletins for the construction industry.
The blocked merger has also saved around 150 jobs at the Liverpool-based publishing company because Emap would have moved the offices to the South East.
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