Five days away from the New York primary, independent voters protested the state's closed primary process, which they say will exclude nearly 3 million residents from voting on April 19 — a particularly damaging prospect for non-establishment candidates like Donald Trump and Bernie Sanders.

Dozens of demonstrators, who support Sanders, gathered on the steps of New York's City Hall on Thursday, calling on lawmakers to open up New York's primary election process, which would allow any registered voter regardless of their political affiliation to vote for the candidate of their choice.

Organizers of the rally, led by nonpartisan groups IndependentVoting.org, the New York City Independence Clubs, and Open Primaries, blasted the state's closed primary as "undemocratic," noting that the voters most disenfranchised by this process are young people and minorities. Some 37 percent of New Yorkers under 30 identify as independent, while 15 percent of African American voters and 22 percent of Latino voters statewide are also unaffiliated with any major party, according to an analysis of voter data compiled by collection firm Prime New York.

"This is a crucial issue of our time," said Jackie Salit, president of IndependentVoting.org, which advocates for open primaries, nonpartisan redistricting, and independent election supervision. "No one should be forced to join a political party as a condition for voting that is un-American, that is undemocratic."

Across the US, at least 43 percent of Americans label themselves as political independents, far exceeding those who identify as Democrats (30 percent) and Republicans (26 percent), according to a 2015 Gallup poll. The majority of independents still lean either more Republican or Democrat when pressed, but in recent years there has been a swell in those who don't affiliate outright with either major party, and this has corresponded with other surveys showing high levels of frustration with Congress and partisan politics.

There are nearly 3 million out of 10.7 million active voters in New York state who are not registered with either major party, according to state elections board figures. Not only will these voters be precluded from voting in the state's primary on April 19, but it's also already too late for them to change party affiliation if they did decide they wanted to back a Republican or Democratic candidate. The cut-off for residents to change party registration was October 9, 2015, more than six months before the primary. Even Republican frontrunner Donald Trump's children only recently discovered this, and won't be able to vote for their dad on Tuesday. New voters in New York had until March 25 to register.

At a Sanders rally in New York City's Washington Square Park on Wednesday night that, according to the campaign, drew some 27,000 people, the senator denounced the state's closed primary process, which potentially shuts out a large portion of his biggest support base: Millennials.

"We have a system here in New York where independents can't get involved in the democratic primary," he said. "Where young people who have not previously registered and want to register today just can't do it. So this is going be a tough primary for us."

Supporter Lorraine Sangre, who was formerly a registered independent but switched to the Democratic Party to vote for Sanders, said Wednesday she had "made a point" of doing her own research on electoral rules ahead of the re-registration deadline because she had not seen any government advertisements or information about the process being given to voters.

"There's so many things about the whole process that are intentionally made to be difficult to disenfranchise people," she said. "It doesn't seem accidental at all."

Trump, too, has been a vocal critic of party and state rules that have prevented his supporters from voting for him in several primaries this year. His adviser and special counsel Michael Cohen argued this week that, in New York at least, the rules preventing independents and Democrats from supporting the frontrunner won't hurt him too much. "Don't worry about Mr. Trump. He's around 50-plus percent in New York. This is his hometown," Cohen said, before acknowledging that he won't be able to vote for Trump in the New York state primary either.

Independent and unaffiliated voters in New York have long called for a dilution of the power the Republican and Democratic parties have over state and federal election systems. Those calls grow louder in presidential election years. As it currently stands, the major parties are in charge of determining primary election rules and procedures, which vary from state to state, and some are more prohibitive for independents than others. There are some 11 states, including New York, that have closed systems, while the rest hold open primaries or have a hybrid system that allow independents to vote in some capacity. Some protesters Thursday said that that the closed system is archaic and only serves candidates who are already firmly ensconced in the establishment.

"New York has some of the worst election laws in the United States [including] the most restrictive registration law in the country for independent and unaffiliated voters," Cathy Stewart, citywide coordinator for New York City Independence Clubs, said. "The state has a completely closed process at all levels; state, city, and federal, so independent voters are regularly excluded from all rounds of the electoral process."

"Taxpayers are footing the bill for these elections and some can't even participate in them," she added.

Party operatives argue that opening up party primaries to independent voters could result in "party raiding," where a member of one party strategically votes for the weakest candidate in the opposing party's primary, thereby giving their candidate a better chance of winning in the general election.

Concerns about the practice of party raiding were re-raised in 2008 after conservative talk show host Rush Limbaugh launched "Operation Chaos," in which he urged Republicans to vote for Hillary Clinton over Barack Obama in order to prolong the Democratic primary and encourage infighting. Yet, "there is no evidence that crossover party raiding happened as a result of Operation Chaos," according to Renée Paradis, Counsel for the Democracy Program at NYU's Brennan Center for Justice.

"The information requirements and levels of voter sophistication to accomplish cross-party raiding are daunting; and the opportunities for pay-off are scarce," Paradis told lawmakers at a hearing of the New York State Senate Elections Committee in 2009, intended to weigh the consequences of shortening the deadlines for enrolling in a political party before a primary.

Although party raiding does not significantly impact the Republican and Democratic parties, some argue that in states like New York, closed primaries are intended to help protect smaller parties like the Green and Working Families parties.

Assemblyman Fred Thiele, the New York legislature's only Independent member, said at Thursday's protest that the "laws are skewed against independents," and that was part of the reason for depressed turnouts in recent elections, especially among young voters.

Thiele, who authored one a bill to open the presidential primary to independents, said that independents "have to work extra hard" in a closed electoral system.

That is perhaps why calls from Bernie Sanders and Donald Trump to overhaul the electoral system have resonated particularly strongly among unaffiliated voters. So far in 2016, both candidates have done particularly well in states that hold open primaries or have mixed systems where independents can vote.

And for Sanders in particular, young people and independents are two groups that have held his insurgent campaign aloft. In primary states like New Hampshire, Massachusetts, Michigan, and Wisconsin, Sanders won between 66 and 73 percent of independent voters. But come Tuesday, voters from both of those demographics will be stymied by New York's electoral rules.

Trump who is also considered an establishment outsider, has also been polling better than his Republican counterparts with independents across primary states in the US as well. Yet according to recent polling, Trump maintains leads of up to 30 points in New York among registered Republicans, so any setbacks he suffers from a lack of independent participation will likely not hinder his path to victory in the state.