Federal prosecutors have subpoenaed Trump Media & Technology Group and “certain current and former TMTG personnel,” according to a regulatory filing Friday by Digital World Acquisition, the special-purpose buyout firm that has a tentative merger agreement with Trump Media. Grand jury subpoenas are usually issued in connection with a potential criminal investigation. The filing said the Securities and Exchange Commission also issued a subpoena to Trump Media this week. A few days earlier, Digital World revealed that it, too, had received a subpoena from federal prosecutors in Manhattan along with similar subpoenas served on its board of directors. The grand jury subpoenas appear to be related to earlier SEC subpoenas for Digital World that sought communications about potential merger talks with representatives of Trump Media before Digital World’s initial public offering in September. The regulatory filing on Friday said the grand jury subpoenas served on Trump Media “seek a subset of the same or similar documents requested in subpoenas to Digital World and its directors.” The widening investigation threatens to delay the completion of the merger, which would provide Mr. Trump’s company and social media platform Truth Social with up to $1.3 billion in capital, in addition to going public. The SEC investigation focused on whether there were serious discussions between Digital World’s leadership and Trump Media before the special purpose acquisition company, or SPAC, went public in September and, if so, why those conversations were not disclosed in regulatory filings. SPACs, which raise money to go public in hopes of finding a merger candidate, aren’t supposed to have a takeover goal in mind when they raise money from investors. Regulators also requested information about trading activity in Digital World’s securities before the merger was announced in October. A few weeks before the merger was announced, there was a big spike in trading of Digital World Warrants — a type of security that gives the holder the right to buy shares at a set price. Trump Media is based in Sarasota, Florida and is led by Devin Nunes, the former Republican congressman who became CEO this year. Mr. Trump, who has a licensing deal with the company, is president. In a statement, Trump Media said it “will continue to fully cooperate with investigations into our proposed merger and will comply with calls we have recently received, none of which were directed to the company’s chairman or CEO.” It is unclear which current and former Trump Media staff received calls. Truth Social, a Twitter-like platform, remains the company’s flagship product. Mr. Trump has, in recent months, become a frequent poster on the platform. This week, he used the platform repeatedly to criticize former White House aide Cassidy Hutchinson’s testimony before a congressional committee on Jan. 6. Trump Media called Truth Social a “free speech” alternative to Twitter, which permanently banned the former president from using its platform after the January 6, 2021 attack on Capitol Hill. Maggie Haberman contributed reporting.