D.C. voters heading into the polling place on Tuesday will be asked to vote for two candidates for the D.C. Council’s At-Large seats. There are six candidates running: a Democrat, a Republican, a member of the Statehood Green Party and three independents.

The diversity isn’t a coincidence. D.C.’s Home Rule Charter—the city’s constitution—explicitly states that of the four at-large seats on the Council, “not more than two of the at-large members shall be nominated by the same political party.” In heavily Democratic D.C., that means two of the four at-large seats are reserved for anyone but Democrats.

But where does this quirky requirement come from? Congress.

“The real thinking was that home rule would be healthier down the road if there was some minority party representation,” explains Nelson Rimensnyder, who was an aide to Charles Diggs, the Michigan Democrat who helped write the bill in 1973 that gave D.C. an elected mayor and Council. “It was well known that the District was a one-party town.”

In short, it was a means to ensure a diversity of viewpoints in a city where one political party predominates. And although the provenance of the set-aside seats is unique for D.C., and they generally are rare for state or city legislatures, there are a few places that operate under similar systems.

Philadelphia’s 1951 Home Rule Charter also includes a requirement that two of its City Council’s seven At-Large seats be set aside for non-majority political parties. In Connecticut, a similar law enacted in 1949 guarantees minority party representation on boards, councils and commissions. For a three-person board, for example, only two members can be of the same party; on a nine-member commission, only six can be of the same party.

“Connecticut’s minority representation rules, though not perfect, serve important goals,” read an editorial last year in the The Ridgefield Press. “One is simply balance—ensuring a place for a different perspective, dissenting viewpoints. But equally important is the function of keeping the minority party—in Ridgefield, the Democrats, but the Republicans in New Haven—active and serious, ready with politically experienced officials to offer as an alternative should the majority party’s leaders mess up and need to be replaced.”

The first Republican to be elected to the D.C. Council as an At-Large member was Rev. Jerry Moore in 1975, who himself cheered the set-aside seats Congress had created for his party. “I believe we need a strong two-party system,” he said. And Edmund Pendleton, then the chairman of the D.C. Republican Committee, predicted that having access to two seats would help the party’s chances in the long run.

“You can have a heavily imbalanced situations in the Council if it becomes a little Democratic caucus,” he said. “We don’t think we’ll win a majority of the Council seats, but it’s a great chance for the city. After a few elections when people see the only real contest is in the Democratic primary, they’ll start voting Republican to shake up City Hall.”

Did that happen? Sort of.

In 1975, the first Council to be elected had a Republican (Moore) and a Statehood Green (Julius Hobson) occupying the set-aside At-Large seats. Moore left the Council in 1985, and was replaced by Carol Schwartz, a Republican who served until 1989 and then again from 1997 to 2009. (In 1994, Schwartz ran for mayor against Marion Barry, and logged 42 percent of the vote.) That was the golden era, so to speak, for Republicans on the Council: along with Schwartz, David Catania also occupied an At-Large seat.

But in 2004, Catania became an independent over objections to George W. Bush’s stance on same-sex marriage. Ever since Schwartz left the Council in 2009, there haven’t been any Republicans sitting in either of the set-aside At-Large seats—nor Statehood Greens, or Libertarians. But there have been a string of independents, including the two currently on the Council: David Grosso and Elissa Silverman.

That bothers Rimensnyder, himself a member of the D.C. Republican Party who is challenging Del. Eleanor Holmes Norton this year. He says that independents aren’t really a member of a political party, and more often than not, they are Democrats who leave their party only to run for the At-Large seats. (Both Grosso and Silverman did.)

“It’s been so convenient for Democrats to stay Democrats and then become a so-called independent,” he says. “I think it should be challenged in court.”

The D.C. GOP did file challenges in 2008 and again in 2013, but they have not yet succeeded in enforcing their interpretation of the charter, which would only allow formal members of the official minority parties—Republican, Statehood Green and Libertarian—to run for the At-Large seats. This year, the candidates for the At-Large seat include Republican Ralph Chittams and Statehood Green David Schwartzman.

On the other side, some local Democrats want to see the set-aside seats scrapped altogether. They say that if candidates from minority parties want a seat on the Council, they should have to win it fair and square. They also argue that the rule favors parties that have a very small number of registered voters in the city—as of October, there are just over 30,023 Republicans, 3,785 Statehood Greens and 1,295 Libertarians out of 491,733 registered voters in the city. The editorial board of The Washington Post agreed with the Democrats in 2014, opining:

There is something essentially undemocratic about setting aside seats. There is generally less competition for them and those who get elected do so with fewer votes. Better systems exist in other cities that open up the process without the charade of candidates pretending to be something they aren’t. Some jurisdictions, for example, have primaries in which candidates of all parties run, with the top two winners advancing to the general election. Or there is the practice of non-partisan elections, a proposal that was on the table for the District when Home Rule was approved but that was unwisely rejected in favor of the set-aside seats.

Rob Richie disagrees. He’s the executive director of Fair Vote, which advocates for electoral reforms to increase political participation and diversity.

“It’s not the best way to do it, but it’s better than not doing it,” he says of D.C.’s set-aside At-Large seats. “I believe you make better decisions after hearing more voices.”

Richie does think more U.S. jurisdictions should seriously consider changing how they run their elections to better incorporate diverse voices and make sure as many voters as possible feel truly represented. That would mean moving away from the winner-take-all system that predominates in the U.S. For examples, he says elected officials would have to look no further than continental Europe.

“They all use some non-winner-take-all system that more reliably and more fairly does what D.C. does. That sense of representing more people and having a legislature that reflects majority and minority opinions is the norm,” he says. “We’re the real outlier.”

Cambridge, Massachusetts runs elections for its nine-member Council under a system of proportional representation. Voters can choose any number of candidates on the ballot, but they have to rank them in order of preference. That means a majority of voters are assured that their top choices are elected, but not to the detriment of candidates preferred by a smaller number of voters.

“So you end up with a very representative group of people,” says Richie.

Would that fly in D.C.? A variation known as ranked-choice voting has been proposed in the D.C. Council — and has gotten a nod of support from the Washington Post—but hasn’t gone much further than that. So, for now, the set-aside At-Large seats remain.

This story originally appeared on WAMU.