European Union anti-trust regulators on Friday said they are investigating whether state-owned ChemChina's $43 billion buyout of Swiss chemical giant Syngenta could reduce competition in crop protection products.

The Commission said the $43 billion merger could harm competition as Syngenta and ChemChina, through its agrichemical subsidiary Adama Agricultural Solutions had overlapping portfolios in the production of crop protection products like herbicides, insecticides, fungicides and plant growth regulators.

"This deal would lead to the combination of a leading crop protection company with one of its main generic competitors. Therefore, we need to carefully assess whether the proposed merger would lead to higher prices or a reduced choice for farmers," said Margrethe Vestager, EU Competition Commissioner.

The Commission will decide by March 15 whether to approve the deal.

The announcement was expected after Syngenta said earlier this week that regulatory approval of its proposed acquisition by ChemChina was likely to be delayed into early 2017 as regulators seek more information amid a consolidation wave in the sector.C

ChemChina submitted a proposal to the Commission in September, including a plan to divest some $20 million worth of assets from Adama Agricultural Solutions, a Beijing-based source told Reuters.

Syngenta's shares plunged more 9 percent on Monday after the European Commission said the companies had not allayed its concerns over the deal, raising the prospect of a longer investigation.