Regulators want to block the Staples-Office Depot merger, and now both stocks are crashing

Shares of both Office Depot and Staples are each down double digits on Monday after the Federal Trade Commission announced it is suing to block the transaction that would make for the country's biggest office supply company.

Office Depot shares fell by 17% in mid-day trading on the news the regulator would seek to block the deal.

Staples stock slumped for more than 12% on the news.

Here's what the FTC said, as part of its broader statement:

"The Commission has reason to believe that the proposed merger between Staples and Office Depot is likely to eliminate beneficial competition that large companies rely on to reduce the costs of office supplies," said FTC Chairwoman Edith Ramirez. "The FTC's complaint alleges that Staples and Office Depot are often the top two bidders for large business customers."

It's not the first time a multi-bilion dollar deal that would have made for big benefits for investors was squashed by regulators in 2015.

Comcast gave up its bid to buy Time Warner in April amid regulatory concerns, as well.