The Democratic National Committee (DNC) adopted a new rule on Friday aimed at keeping outsider candidates like Sen. Bernie Sanders (I-Vt.) from trying to clinch the Democratic presidential nomination in 2020.

The new rule, adopted by the DNC's Rules and Bylaws Committee, requires all Democratic presidential candidates to be a member of the Democratic Party, Yahoo News reported.

A presidential candidate running for the Democratic nomination must be a member of the party, accept the Democratic nomination and "run and serve" as a member.

Sanders, who has maintained his status as an independent, fought a tough primary race for the Democratic nomination against eventual presidential candidate Hillary Clinton in 2016.

A source familiar with the discussions told Yahoo News, however, that the rule wasn't targeted at Sanders.

Randi Weingarten, president of the American Federation of Teachers and DNC member, posted a photo on Twitter Friday of the rules change at the meeting in Providence, R.I.

"At the time a presidential candidate announces their candidacy publicly, they must publicly affirm that they are a Democrat," the rule says.

In March, the DNC voted to acknowledge a need to reduce the influence of so-called superdelegates in presidential primaries - the unelected delegates who may support any candidate for the party's nomination, regardless of their state's victor.

Yahoo News reported that the committee did finalize a vote on superdelegates and will decide in August.