The US Internal Revenue Service (IRS), has announced that same-sex couples who are legally married will now be recognised for federal tax purposes, irrespective of their home state’s legal position on equal marriage.

The change announced this week by the IRS and the US Treasury is the largest federal rule change to have come out of June’s Supreme Court ruling which struck down the Defense of Marriage Act (DOMA), which previously defined marriage as specifically between one man and one woman.

“Today’s ruling provides certainty and clear, coherent tax filing guidance for all legally married same-sex couples nationwide. It provides access to benefits, responsibilities and protections under federal tax law that all Americans deserve,” said Secretary Jacob J. Lew. “This ruling also assures legally married same-sex couples that they can move freely throughout the country knowing that their federal filing status will not change.”

Under the ruling, same sex couples will be treated as married for all federal tax purposes, including income  and gift and estate taxes. The ruling applies to all federal tax provisions where marriage is a factor, including filing status, claiming personal and dependency exemptions, taking the standard deduction, employee benefits, contributing to an IRA, and claiming the earned income tax credit or child tax credit.

A key part of DOMA was struck down, opening up over 1,100 federal benefits to married same-sex couples.

Many have taken the IRS’ decision as a sign of how quickly the US Government will move to treat same-sex couples equally.

The largest retailer in the US, Walmart, earlier this week announced that it is to offer health insurance benefits to same-sex domestic partners beginning next year.