Comco, Switzerland’s competition commission, and the authority overseeing the Swiss stock exchange are also looking into merger, which would create the world’s largest cement maker.
The boards of the two companies agreed to the merger earlier this month, with the headquarters of the new mega-firm to be located in Switzerland.
But on April 7th, the day the union agreement was announced, shares in Holcim jumped 7.3 percent.
Individuals are suspected of abusing their position inside the company to trade shares on the stock exchange before the accord was unveiled, weekly newspaper SonntagsZeitung reported on Sunday.
“The prosecutor’s office has been informed of the facts and is examining whether conditions are met to open an investigation,” the office said in a statement issued on Monday.
The office declined to make further comments on the affair.
The two cement makers confirmed merger talks were at an “advanced” stage on the Friday before an agreement was formally announced.
And on the Sunday before this, Le Figaro newspaper announced the boards had agreed to join forces the day before but it did not cite a source
Holcim and Lafarge reported revenues totalling €31.9 billion ($44.2 billion).