When it comes to marriage, the U.S. tax code is roughly neutral: The number of people penalized for being married is roughly the same as the number who benefit from it.

The same is not true for social welfare programs, such as Medicaid, food stamps or housing assistance, which can impose significant financial penalties on recipients who are married, according to new research from the R Street Institute, a Washington think tank.

In some cases, that creates major disincentives for low-income couples—especially those who are already living together—to tie the knot.

“Historically, low-income couples have faced especially onerous marriage penalties, because most safety-net benefits are means-tested (with steep phase-out rates or even cliffs)” applied on those who are married, researchers Douglas J. Besharov and Neil Gilbert wrote. “Marriage could easily reduce or end the benefits of a single parent with children.”

Read the article “How Welfare Programs Penalize Marriage” on blogs.wsj.com.