A government department responsible for data protection laws has shared the contact details of hundreds of journalists.
The Department for Digital, Culture, Media and Sport emailed more than 300 recipients in a way that allowed their addresses to be seen by other people.
The email - seen by the BBC - contained a press release about age-checks for adult websites.
Digital Minister Margot James said the incident was "embarrassing".
She added: "It was an error and we're evaluating at the moment whether that was a breach of data protection law."
In the email sent on Wednesday, the department said new rules would offer "robust data protection conditions", adding: "Government has listened carefully to privacy concerns."
A DCMS Spokesperson said: "In sending a news release to journalists an administrative, human error meant email addresses could be seen by others. DCMS takes data privacy extremely seriously and we apologise to those affected."
It is the second time this month a government department has made a mistake of this kind.
DCMS has just announced that the porn filters are coming online on July 15, in an email that cc's every media and technology journalist in Britain— alex hern (@alexhern) April 17, 2019
The Home Office previously admitted breaching data protection rules when it launched the Windrush compensation scheme.
It shared the contact details of Windrush migrants in an email about the scheme.
An internal review was launched and Immigration Minister Caroline Nokes apologised "unreservedly" for what she said was an "administrative error".
The data breach affected five batches of emails, each with 100 recipients, Ms Nokes added.