The Democratic National Committee adopted a new rule Friday aimed at preventing non-Democrats, such as independent U.S. Sen. Bernie Sanders of Vermont, from seeking the party’s 2020 presidential nomination, reports said.

The rule change, adopted at a DNC meeting in Providence, R.I., requires all candidates for the party’s nomination to “run and serve” as Democrats, Yahoo News reported.

Some supporters of Sanders -- who caucuses with the Democrats despite declining to declare a party affiliation -- say the move was motivated by “spite” after Sanders gave Hillary Clinton a run for her money during the Democratic primaries in 2016.

But a source told Yahoo News it was actually part of a push to limit the power of so-called superdelegates -- which, ironically, has long been a goal of Sanders.'

Sanders, who describes himself as a democratic socialist, ultimately lost the nomination to Clinton when superdelegates from states he won chose not to vote for him at the party's 2016 convention in Philadelphia.

DNC Chairman Tom Perez on Tuesday floated a proposal to eliminate superdelegates on a presidential primary’s first voting ballot, the Washington Post reported. Party leaders would vote only if the contest required a second ballot.

“You had superdelegates voting for Hillary Clinton in states that I won pretty handsomely,” Sanders told Post this week. “And now there is agreement among Tom Perez and our people, and a lot of the Clinton people, to say we should reduce the number of superdelegates.”

Still, the rule change left some Sanders supporters puzzled as to why Democrats would want to make their party less inclusive.

“We just came off a devastating presidential loss in 2016,” Mark Longabaugh, a senior adviser to Sanders’ 2016 campaign, told Yahoo News. “It would seem to me the actual impetus would be to expand the Democratic Party. I, just for the life of me, don’t see any motivation for this beyond personal spite.”

"I just for the life of me don’t see any motivation for this beyond personal spite.” — Mark Longabaugh, senior adviser to Sanders’ 2016 campaign

A photo of a printout of the rule change was shared Friday in a Twitter message posted by DNC member Randi Weingarten, president of the American Federation of Teachers.

“At the time a presidential candidate announces their candidacy publicly, they must publicly affirm that they are a Democrat,” the printout says. "Each candidate must then affirm in writing that they: A. are a member of the Democratic Party; B. will accept the Democratic nomination; C. will run and serve as a member of the Democratic Party.”

But Sanders may be protected from the change thanks to a resolution passed in his home state, by which he is considered a Democrat, “for all purposes and [is] entitled to all the rights and privileges that come with such membership at the state and federal level,” Politico reported.

DNC members will meet in August for a final vote on the proposal to eliminate superdelegates, Yahoo News reported.