The Department of Justice is suing to block Halliburton from buying Baker Hughes

It's official: the Department of Justice is suing to block Halliburton from buying Baker Hughes.

Reports on Tuesday said the DOJ was preparing to file an antitrust lawsuit to stop the deal. Halliburton is the second-largest oilfield services company, and Baker Hughes is the third-largest.

In a statement on Wednesday, the DOJ said the merger would "eliminate significant head-to-head competition in oilfield services industry."

The antitrust concerns relate to whether smaller companies would be able to compete effectively with the combined giant.

"The proposed deal between Halliburton and Baker Hughes would eliminate vital competition, skew energy markets and harm American consumers," said Attorney General Loretta Lynch in the statement. "Our action makes clear that the Justice Department is committed to vigorously enforcing our antitrust laws."

The deal is worth $25 billion, down from $35 billion after Halliburton shares fell, according to Reuters. It was first announced in November 2014.

Shares of both companies spiked in trading.

More to come ...