Bloomberg’s position is notable because he considered running as an independent candidate in the 2016 presidential election before ultimately deciding against the move. Last summer, reports said that Bloomberg, 76, was also considering running for president in 2020, although he previously told associates that if he were to to do so, he would likely run as a Democrat.

“Now I have never been a partisan guy—and it’s no secret that I looked at an independent bid in the past. In fact I faced exactly the same decision now facing others who are considering it,” Bloomberg wrote in a statement on his web site, without naming Schultz. “The data was very clear and very consistent. Given the strong pull of partisanship and the realities of the electoral college system, there is no way an independent can win. That is truer today than ever before.”

Schultz’s comments about considering an independent candidacy drew volumes of criticism on Twitter along with calls for boycotting Starbucks. Donors to the Democratic party also blasted Schultz, concerned that he could draw votes away from a Trump challenger. Bloomberg’s statement also argued such an outcome was likely.

“In 2020, the great likelihood is that an independent would just split the anti-Trump vote and end up re-electing the President. That’s a risk I refused to run in 2016 and we can’t afford to run it now,” Bloomberg said. “We must remain united, and we must not allow any candidate to divide or fracture us. The stakes couldn’t be higher.”

The prospect of Schultz running as an independent candidate has proven so unpopular that it has even drawn mockery from consumer product brands. On Monday, the Twitter account for Pop-Tarts also announced it was exploring a presidential run in 2020. Steak-umm, which previously had signaled its intention to run, called Pop-Tarts’ candidacy a “declaration of war.”