Grimm's threat came Tuesday night at the end of an interview on President Obama's State of the Union speech, which he called "divisive," NY1 reported.
NY1 reporter Michael Scotto then tried to ask Grimm about a federal investigation into his 2010 campaign fundraising but was cut off. Grimm has not been charged.
"I'm not speaking to you off-topic, this is only about the president," Grimm said then left.
The reporter, Michael Scotto, wrapped up his interview with, "So Congressman Michael Grimm does not want to talk about the allegations concerning his campaign finances," then signed off.
However, the camera was rolling and Grimm returned to Scotto, NY1 said.
"Let me be clear to you: If you ever do that to me again, I'll throw you off this [expletive] balcony," said Grimm, a former Marine and former FBI agent.
Scotto said he was trying to ask "a valid question."
"No, no. You're not man enough, you're not man enough. I'll break you in half, like a boy," Grimm said.
Scotto Wednesday tweeted Grimm had apologized by phone, saying he had "overreacted."
"I accepted his apology and I think we're going to move on from here," Scotto told Capital Playbook.
New York Mayor Bill de Blasio Wednesday called Grimm's threat "inappropriate."
In a statement issued after the incident, Grimm said he was "extremely annoyed" because he thought he was doing NY1 "a favor by rushing to do their interview first in lieu of several other requests."
The reporter knew he was pressed for time and was planning to comment only on the State of the Union speech "but insisted on taking a disrespectful and cheap shot at the end of the interview, because I did not have time to speak off-topic," the statement said.
"I doubt that I am the first member of Congress to tell off a reporter, and I am sure I won't be the last," the statement said.
In his statement, NY1 Political Director Bob Hardt said, "It is extremely disturbing when anyone threatens one of our reporters, let alone a U.S. congressman. The NY1 family is certainly alarmed and disappointed by the behavior of Representative Grimm and demands a full apology from him. This behavior is unacceptable."