BuzzFeed said Donald Trump's rhetoric has caused it to terminate a deal with the Republican National Committee (RNC) to run political ads on the site this autumn.
In an email sent to BuzzFeed employees, chief executive Jonah Peretti said BuzzFeed told the RNC on Monday morning that it would not accept Trump ads.
Mr Peretti said the Republican presidential frontrunner's campaign is "directly opposed to the freedoms of our employees in the United States and around the world".
He said Mr Trump's proposed ban of Muslims entering the US would "make it impossible" for some employees to do their jobs.
In an emailed statement, the party's communications director Sean Spicer said "space was reserved on many platforms, but we never intended to use Buzzfeed".