Echoing critiques made by Bernie Sanders and supporters of his presidential campaign, 14 progressive organizations are urging the Democratic Party to scrap the superdelegate system, which they say "undermines representative democracy."

The groups, including Democracy for America, National Nurses United, The Other 98%, and Progressive Democrats of America, outline their concerns in a letter, which was obtained by Politico, to the Democratic National Committee (DNC), the DNC Rules Committee, and the delegates to the Democratic National Convention.

They're calling on the party to take action to get rid of the system that allows state party elites and elected officials to back the candidate of their choosing when the committee convenes in Philadelphia July 25-28.

"The superdelegate system," the letter (pdf) states, "is unrepresentative, contradicts the purported values of the party and its members, and reduces the party's moral authority."

The system "dilutes the voters' say over the party's platform," and, as "a near super-majority of superdelegates are men," it undermines the Party's pledge to gender equity.

The letter also criticizes the average age of the superdelegates as being far older than the average Democrat, and the fact they they appear "to skew the party away from appropriate representation of communities of color."

The groups' ask is that "moving forward, the DNC retain at least the current total number of delegates, inclusive of superdelegates–4,770–for future national conventions, but allot all of them to states, territories, and Democrats abroad through the rubric that governs pledged delegate allotments, and require that all of them be selected through popular primary and/or caucus processes."

Politico reports that the letter is "yet another sign that liberals and former Sanders supporters remain keen on pushing the party to follow through on a key plank of the Sanders campaign."

Sanders, for his part, has called the system "problematic."

Begun in 1984, and only existing in the Democratic Party, the system includes approximately 712 superdelegates out of roughly 4,700 delegates. These superdelegates can back whomever they choose, regardless of who their state voted for in its primary or caucus, and they are empowered to change their mind at any point before the convention.

Author and RootsAction.org co-founder Norman Solomon has described them as "pillars of the Democratic Party establishment," while Michael Winship, senior writing fellow at Demos and president of the Writers Guild of America-East, wrote that "superdelegates symbolize something that has to go: the entrenched, inside-the-Beltway embrace of power and influence by the Democratic illuminati that does little for the poor and middle class and everything for the one percent that writes the big checks."

Sanders' call to overhaul the system appears to have the backing of some of his fellow members of the U.S. Senate. In addition, several states—California, Nebraska, and Maine—are calling for a revamp of the superdelegate system as well.