Dish Network is also competing to buy Sprint and has argued that regulators should ensure that an American company owns Sprint's communications networks.
The FCC is reviewing whether allowing the SoftBank deal would be in the public's interest, while a committee made up of the Justice Department, Homeland Security Department and other agencies is reviewing whether the merger poses a threat to national security.
In a bid to address national security concerns, SoftBank has promised not to use Chinese telecommunications equipment in its networks. The Wall Street Journal reported on Wednesday that the company has also agreed to allow the U.S. government to approve one of the directors on Sprint's board. The director would oversee national security issues for the company.