Sprint is now the US's fourth largest wireless carrier, while T-Mobile sits in third place, behind the mobile network duopoly that is Verizon and AT&T.
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.
SoftBank will propose ending the talks as early as Tuesday, Nikkei said. The companies had been ironing out final terms of the merger in the hopes of announcing a deal in mid- to late November, people familiar with the matter told Bloomberg earlier this month.
Sprint shares sank as much as 13 percent in NY trading, while T-Mobile fell as much as 5.9 percent.
But Softbank, Sprint's owner, seems to have soured on the idea. These two companies came close in 2014 about the merging, but later due to some regulatory concerns called it off.
Sprint and T-Mobile have discussed a merger for years with many fits and starts, and it was unclear whether the companies will ultimately return to the table, the people said.
Deutsche Telekom and T-Mobile declined to comment.
If the discussions fall apart then it would be the second time a failed attempt made in merging T-mobile and Sprint.
Deutsche Telekom, based on Bonn, Germany, has maintained throughout the talks this year with SoftBank that it should maintain control of the combined company. Others think he wants to invest ever more in Sprint, the better to realize his dream of connecting devices, humans, and other machines in a single artificial intelligence.