Undocumented immigrants attend a news conference of families facing deportation in November 2014 in Newark, N.J. (John Moore/Getty Images)

A group of big-city mayors led by New York's Bill de Blasio and Los Angeles's Eric Garcetti announced plans Friday to file a legal brief supporting President Obama's executive actions on immigration, which are being challenged in federal court by 25 states. D.C. Mayor Muriel Bowser is among those who signed onto the brief.

The brief will argue that "the public interest across the country is served clearly and overwhelmingly by implementing immigration reform by executive action," the mayors said in a statement. They made the announcement at the U.S. Conference of Mayors, which is taking place in Washington.

"Delaying implementation of the President’s executive action will further hurt our families, negatively impact our economies, and create unnecessary insecurity in our communities,” de Blasio said in a statement.

Obama announced in November that he would use his executive powers to protect as many as 4 million illegal immigrants from deportation and make other changes to border control policies designed to focus federal resources on violent and repeat criminals. The president said he acted after Congress failed to approve a comprehensive immigration reform bill last summer.

But Republicans have challenged the actions, calling them unconstitutional. The lawsuit from 25 states, led by Texas, argues that the "unilateral suspension of the Nation’s immigration laws is unlawful."

The mayors of Atlanta, Baltimore, Chicago, Houston, Denver and San Francisco also joined the brief in support of Obama's actions. So far 28 mayors in all have signed on.