FILE PHOTO: Democratic 2020 U.S. presidential candidate and former Vice President Joe Biden speaks during a campaign stop in Philadelphia, Pennsylvania, U.S., May 18, 2019. REUTERS/Mark Makela/File Photo

WASHINGTON (Reuters) - Seeking to cull its crowded 2020 presidential field, the Democratic Party will make it tougher for candidates to qualify for a third debate scheduled for September.

The party will require contenders to meet both a higher polling standard and a larger fundraising target, the Democratic National Committee said on Wednesday.

In the first two debates, scheduled for June and July, contenders have to meet just one of the two criteria, leaving open the possibility that as many as 20 of the 24 announced Democratic candidates could be on stage.

Under the new standards, candidates must reach 2 percent or higher in four public opinion polls, conducted nationally or in early voting states, and must demonstrate they have received contributions from 130,000 unique donors as well 400 unique voters in 20 states. The tougher criteria are double those of the first two debates.

The third debate will be held on Sept. 12 and may be extended to the following evening if enough candidates qualify. The debate, whose location has yet to be announced, will be sponsored by ABC and Univision.

The same criteria will apply for the fourth debate in October, the DNC said.

The sprawling field has made it difficult for lesser-known candidates to register in the minds of Democratic voters, with several polling at 1 percent or less nationally.

Late-announcing candidates such as New York Mayor Bill de Blasio and U.S. Senator Michael Bennet of Colorado are among those who have struggled to meet the initial debate criteria. Bennet was critical of the winnowing process in an interview this week with Fox News.