Speaking to the BBC's Politics Live, Laura Kuenssberg claimed to have received tip-offs from those with knowledge of early votes cast in the general election, during a discussion about poor weather impacting voter turnout.
She went on to describe what sources had told her about the results of postal ballots already counted.
The Electoral Commission responded to the incident shortly afterwards, writing on Twitter: “It may be an offence to communicate any information obtained at postal vote opening sessions, including about votes cast, before a poll has closed.
“Anyone with information to suggest this has happened should report it immediately to the police.”
When asked if this applied to Ms Kuenssberg’s statement, the watchdog repeated its assertion that anyone communicating information obtained at postal votes may have breached electoral law.
Candidates are allowed to attend postal vote opening sessions, or can appoint a representative to attend on their behalf. Everyone in attendance has a duty to maintain secrecy, the watchdog said.
Ballot papers are kept face down while votes are opened and it is forbidden to attempt to see how ballots have been marked or to keep a count. Postal votes are not counted until 10pm on the day of the election.
“The parties, they’re not meant to look at it but they do kind of get a hint,” Ms Kuenssberg said on Wednesday morning, before revealing what she had been told by those who claimed knowledge of their contents.
Broadcasting regulator Ofcom has strict electoral rules around broadcasting or publishing the results of votes or opinion polls on election day before 10pm over concerns that doing so could influence voters’ decisions.
A BBC spokesperson said: “The BBC does not believe it, or its political editor, has breached electoral law.”