Shares of Sprint on Monday fell 3.6% to $7.73, and T-Mobile dropped 2.2% to $29.75.
According to a report from The Wall Street Journal, Sprint Chairman Masayoshi Son and CEO Dan Hesse were surprised by the level of opposition they found when meeting with the Federal Communications Commission. That opposition made the two take a step back and reconsider the possible bid, the Journal said.
The FCC and Department of Justice have recently signaled that both prefer the current four-carrier U.S. wireless market to a three-carrier market. Sprint may yet attempt a merger, but will likely take several weeks to prepare its strategy and regulatory arguments.
Sprint hasn't yet responded to requests for comment.