Sprint and T-Mobile may not merge. According to Nikkei, Sprint's owner, Softbank, plans to call off merger negotiations with T-Mobile because the two companies can't agree on the ownership scheme.

The two companies have been in talks for months, and Softbank had hoped to combine the two companies as early as 2013.

According to Nikkei, SoftBank is expected to approach T-Mobile owner Deutsche Telekom as early as Tuesday to propose ending the talks. They had reached a broad agreement to integrate T-Mobile and Sprint -- the third- and fourth-largest carriers in the U.S. -- and were ironing details.

The German parent had insisted on a controlling stake, according to the report. Some at SoftBank were initially amenable as long as the Japanese company retained some influence. But SoftBank's board discussed at a meeting Friday that the company would not give up control. The decision to call off the talks was reportedly made Monday.

In the U.S., Sprint sits well behind the top two of Verizon Communications and AT&T in scale and subscribers. The hope was that a merger with T-Mobile would reinforce Sprint's customer base enough to let it challenge the duopoly while allowing for more efficient network investment.

SoftBank tried to buy T-Mobile in 2014, but the idea was abandoned amid opposition from regulators.