FILE PHOTO: Twelve Democratic presidential candidates participate in the fourth U.S. Democratic presidential candidates 2020 election debate in Westerville, Ohio, U.S., October 15, 2019. REUTERS/Shannon Stapleton/File Photo

(Reuters) - The number of Democratic candidates on stage for the party’s sixth presidential debate in December is set to be winnowed after stricter rules for qualification were announced on Friday.

The Democratic National Committee, which sets the rules for how candidates qualify for the debates, announced tougher fundraising and polling thresholds for the sixth debate, which will be held on December 19 in Los Angeles.

The criteria will likely mean several lower-tier candidates who have made previous debates and are likely to make the cut for next month’s fifth debate, could struggle to qualify for the December event, which will mark the half-way stage of the Democrats’ debate calendar.

The DNC has continually tightened the qualifying requirements for debates as the year has progressed. The first debate in June was spread over two nights with 20 candidates. The last debate in Ohio earlier this month featured 12 candidates on one night. So far nine candidates have qualified for November’s debate in Georgia.

The stricter criteria will mean candidates trailing the top five 2020 hopefuls – former Vice President Joe Biden, U.S. Senators Elizabeth Warren, Bernie Sanders and Kamala Harris and South Bend Mayor Pete Buttigieg - will be under increasing pressure to make the cut for the December event.

To qualify for the Los Angeles debate, a candidate must hit 4 percent support in at least four DNC-approved polls, which may be national surveys of primary voters or single-state polls in the four early-voting states of Iowa, New Hampshire, South Carolina or Nevada. Alternatively, they can hit 6 percent in two early-state polls.

In addition, candidates must have received donations from at least 200,000 unique donors, with a minimum of 800 unique donors in 20 states, U.S. territories or the District of Columbia. The deadline for qualifying polls and donation targets is December 12. The televised debate on December 19 will be hosted by PBS NewsHour and Politico.

For next month’s fifth debate in Georgia, candidates need 3 percent support in four national or early-state polls and 165,000 unique donors, with at least 600 unique donors in 20 different states, territories or the District of Columbia.