The National Organization for Marriage (NOM) has criticized a Treasury Department decision to allow legally married gay and lesbian couples to file joint tax returns, regardless of whether the state they reside in recognizes such unions.

In a statement released Thursday, Treasury Secretary Jacob Lew said that its “ruling assures legally married same-sex couples that they can move freely throughout the country knowing that their federal filing status will not change.”

“The Treasury Department is grossly overstepping its authority,” NOM President Brian Brown said in blog post. “This is a nation of laws. Only Congress has the authority to change the law.”

“The Obama administration is intent on forcing same-sex 'marriage' on an unwilling public,” he added.

Chris Plante, executive director of the Rhode Island chapter of NOM, told Newsmax TV to expect lawsuits stemming from the decision.

“There will be a myriad of lawsuits,” Plante predicted. “This ruling creates all sorts of confusion and it will result in lawsuits, it will result in states not sure what to do, and the fact of the matter is states do have a right to define marriage as they see fit. This is still in Section 2 of the Defense of Marriage Act.”

“We need to define marriage as one man and one woman not because we are actually creating it but because that's what it is and government has a purpose investing in marriage as one man and one woman because it creates the best place to raise children and the next generation,” he added.

(Related: Gay spouses have equal access to nursing facilities through Medicare, HHS memo states.)