The long-sought merger between two of the four large U.S. wireless carriers is in jeopardy amid reports that the controlling stakeholder of Sprint plans to back out of talks.

Nikkei Asian Review reported Monday that the board of Japanese telecom giant SoftBank Group determined that it would not cede control of a combined Sprint-T-Mobile to Deutsche Telekom, T-Mobile’s parent company.

Reports for weeks indicated that the two sides were close to an agreement on merger terms and that an official announcement was imminent. SoftBank appeared to be receptive to an arrangement that would that would give Deutsche Telekom control as long as it retained some clout in the combined company.

Nikkei, however, reported that the board revisited that decision on Friday and would approach Deutsche Telekom about ending merger talks as early as Tuesday.

CNBC, citing unnamed sources, disputed that the talks could end early this week, but the network and multiple additional reports confirmed that the negotiations hit a snag over governance of the new company and the value of a potential deal.

Even if the companies ultimately agreed on merger terms, it’s unclear whether U.S. regulators would endorse combining the third- and fourth-largest carriers and dramatically consolidate the domestic wireless market.