As of last Thursday, thousands of American families will now be able to claim crucial tax protections and benefits they were previously denied.

In what is arguably the federal government’s most significant rule change since the Supreme Court’s watershed June decision striking down the federal Defense of Marriage Act, the Treasury Department and its Internal Revenue Service have mandated that all legally married same-sex couples be treated as such for the purposes of federal taxation.

Although 37 states still don’t recognize gay marriage, the U.S. government has taken a powerful step in equalizing standards for same-sex couples, no matter what state they call home.

Gay couples legally married in states like Maine but living in states where same-sex nuptials are banned will now be treated no differently than their straight neighbors: At the end of the 2013 tax year, they will be required to file their federal tax returns in the same way that other married couples always have, either as “married filing separately” or “married filing jointly.”

It’s heartening to see the federal government mobilize itself so quickly to implement the Supreme Court decision. Equalizing federal tax standards wasn’t a simple fix, either.

After months of deliberation, the IRS ultimately decided to adapt a 1958 ruling that dealt with a problem involving common-law marriages. As with same-sex marriages, common-law marriages can be contracted in only some states, but many couples in those unions reside in states that don’t recognize them. In 1958, the solution was to base tax policies on where a couple was married, rather than where they live, and this is the same logic used in the decision the IRS announced last week.

The updated IRS standards are a welcome addition and an important step in the nuts-and-bolts implementation of equality.