Black married couples, in general, pay more in tax costs than white, married couples, according to a new report by the Urban-Brookings Tax Policy Center.

Officially, the U.S. tax code is considered race blind, William Gale, one of the report's authors, told NPR.

"But what we've suspected, and what we found, was that the income tax can still impose differential burdens on Black and white households" because of several factors, he said.

Researchers with the nonprofit think tank found that Black couples were more likely to face marriage penalties (46% to 43%) and less likely to receive marriage bonuses (36% to 43%) than white couples.

When tax filers in the U.S. get married they can face a "marriage bonus." That's when a household's tax bill decreases because a couple files jointly and their incomes are disparate enough according to the Tax Foundation, another tax policy nonprofit. Couples can also face "marriage penalties," when the tax bill increases. This generally happens when two people with similar incomes marry and file jointly.

According to the Tax Policy Center, researchers found penalties were larger and more prevalent for Black couples than white couples — 59% to 51% — for households with an adjusted gross income between $50,000 and $100,000.

There's a growing collection of research on race and economics

The report, released this month, is part of a growing body of research into whether institutions and policies reinforce preexisting racial disparities, Gale said.

"There's a broader question about whether institutions and rules and customs that are blind with respect to race are actually neutral with respect to race, or if they reinforce preexisting disparities."

The U.S. tax system is a good example of that, he said.

Gale added the report builds off of earlier work done by legal scholar Dorothy Brown, who wrote The Whiteness of Wealth: How the Tax System Impoverishes Black Americans — and How We Can Fix It. Brown has hypothesized that tax penalties are more frequent and larger for Black couples than white couples.

Brown, a Georgetown Law professor, called the Tax Policy Center's report "an important step forward."

Earlier this year, a study concluded that Black taxpayers face audits from the Internal Revenue Service at a much higher rate compared to other demographic groups.

Brown said it's only beneficial that there are more people studying how race and tax issues are intertwined.

"It's a good thing for American taxpayers, generally, but taxpayers of color specifically."

Key differences can mean a bigger bill for Black couples compared to white couples

When a Black or white couple have the same income, deductions and family structure, they will have the same tax liability, Gale said. But given the average economic differences between white and Black couples, according to the report, Black married couples are still more likely to face penalties and smaller bonuses.

On average, a Black married couple is more likely to have children than their white counterparts, researchers have found. And taxpayers with children generally tend to face larger penalties, according to the Tax Foundation. Additionally, a Black couple's income is likely to be the same to one another whereas a white couple has more income disparity. Both of those factors contribute to the likelihood of more "marriage penalties."

Even when Black couples end up with marriage bonuses, it was smaller than white couples ($1,926 versus $3,304), the research found. The bonus rate, however, was about the same: 2.6 % for Black couples and 2.7 % for white couples.

When focusing on households with adjusted gross income between $50,000 and $100,000, Black couples who faced penalties paid, on average, $1,394 compared to $1,241 for the white couples with penalties. And when it came to bonuses, Black couples received $1,402 versus $1,576 for white couples.

Bringing this research to light helps inform policymakers of the existence of an inherently unequal fiscal system, Gale said.

The first step in making change is "establishing a new set of facts, a new narrative about this. The old narrative is that race and taxes have nothing to do with each other," he said.

Brown said inequities in the tax system doesn't impact only the Black community.

"There's a certain, elite group of high-income, disproportionately white Americans that benefit, and then the rest of us do not," she said.

"I think a race-in-tax analysis is a way towards everybody understanding that there's a really small group of people who benefit and the rest of us are being disadvantaged in a variety of different ways," she said.

Gale said, however, there is no easy fix to making this system more equitable.

"We're really early in the process," he said. "There's a long way to go before we understand the full implications."