Same-sex couples legally married in other US states say they may still file their taxes jointly in Wisconsin, in defiance at the state’s decision that they must file their state tax returns separately.

Following the repeal of Section 3 of the Defence of Marriage Act in June, the Internal Revenue Service recently announced that legally married same-sex couples could file joint federal tax returns even if they live in states like Wisconsin that don’t recognise same-sex marriage.

On Friday however, Wisconsin’s Department of Revenue issued guidelines for such couples, specifying that they would still have to file their state taxes separately.

The decision was based on the state’s 2006 constitutional amendment which says that the state will only recognise marriage between a man and a woman, and means that same-sex couples will also be prohibited from claiming a $480 (£305) tax credit for married couples.

Some couples are reportedly planning to file jointly so that their tax returns are rejected, enabling them to challenge the state’s decision in court.

Pete Oettinger, a certified public accountant with Wegner CPAs in Wisconsin, told The Wisconsin State Journal: “I am well aware that there are several people who will be doing that.”

Oettinger refused to identify any such couples but said he wouldn’t personally be filing their returns because he could be penalised.

Laura Patrick, spokeswoman for Wisconsin’s Department of Revenue, refused to disclose how the guidelines would be enforced, saying such activities were “considered confidential.”

Patrick added: “We expect all taxpayers to voluntarily comply with Wisconsin tax law.”

Katie Belanger, president of Fair Wisconsin, a pro-LGBT group which seeks to reverse the state’s marriage amendment, called the Department of Revenue’s guidelines “extremely disappointing,” saying they “continue to discriminate against same-sex couples.”

Belanger said that her organisation isn’t advocating that same-sex couples file jointly on their Wisconsin returns, but added: “We’re going to keep seeing these situations where couples are treated differently at the federal level than they are at the state level, and that’s going to be a challenge for people and their families.”

In December, a Wisconsin appeals court ruled that the state’s same-sex domestic partnership registry did not violate the state constitutional amendment which bans same-sex marriage.