A massive merger between the London Stock Exchange and Deutsche Boerse looks set to collapse, after the LSE said it wouldn’t sell its 60 percent stake in MTS to appease antitrust concerns.

The whole future of the 29 billion euro merger may be at risk, after the LSE said on Sunay that it would not sell its stake in the Italian fixed-income trading platform. Failure to adhere to the European Commission’s request means the deal is obtain EU approval.

The LSE called the request “disproportionate”, adding that:

“Taking all relevant factors into account, and acting in the best interests of shareholders, the LSE Board today concluded that it could not commit to the divestment of MTS.”

“Based on the commission’s current position, LSE believes that the commission is unlikely to provide clearance for the merger.”

The LSE had already agreed to sell part of its clearing business, LCH, to satisfy competition concerns. The commission’s request for further divestment appeared to be one step too far for the company.

The ‘merger of equals’ has been a source of concern in the wake of Brexit, with many worried about the City of London being tied to Frankfurt as the UK prepares to leave the European Union.