The American Civil Liberties Union joined two other groups in announcing that they were filing suit against key parts of the package. This came hours after Republican Gov. Pat McCrory said in a statement that he had signed the measure, without a ceremony and without journalists present.
Republicans lawmakers who backed the measure said it was meant to prevent voter fraud, which they allege is both rampant and undetected in North Carolina. Independent voting rights groups joined Democrats and libertarians in suggesting the true goal was to suppress voter turnout, especially among traditional Democratic constituencies such as blacks, the young, the elderly and the poor.
"It is a trampling on the blood, sweat and tears of the martyrs -- black and white -- who fought for voting rights in this country," said the Rev. William Barber, president of the state chapter of the NAACP, which is pressing its own legal challenge. "It puts McCrory on the wrong side of history."
North Carolina is among a number of states with GOP strongholds that have passed stricter voter identification laws, redrawn political maps fortifying Republican majorities and reduced early voting under President Barack Obama.
Such states claimed victory after the U.S. Supreme Court, in a 5-4 decision in June, effectively wiped out part of the landmark Voting Rights Act that required federal "preclearance" of election-law changes in all or parts of 15 mostly Southern states with a history of discrimination. The law was enacted during the 1960s to outlaw racial discrimination against voters.
That high court ruling cleared the way for North Carolina's Republican leadership to enact voting law changes without prior federal approval.
However, the Obama administration has signaled that it plans to take on some states over potentially discriminatory changes. U.S. Attorney General Eric Holder said in July that the U.S. Justice Department would challenge a new voter identification law in Texas and previously suggested the department was closely watching developments in North Carolina and in other states.
Once dominated by Democratic centrists, North Carolina has drawn national attention since Republicans who took over the Legislature after the 2010 elections pushed through an ambitious conservative agenda on topics such as abortion, health care and elections.
On Monday, former Secretary of State Hillary Clinton said the North Carolina election law amounted to "the greatest hits of voter suppression." She addressed the issue of voting rights during a speech at the American Bar Association meeting in San Francisco.
Barber called the Republican-backed measure one of the worst attempts in the nation at voting reform. He said the National Association for the Advancement of Colored People considered the package an all-out attack on existing laws long seen as a model of voter participation.
The package would take effect in 2016. It requires voters to present government-issued photo IDs at the polls and shortens early voting by a week, from 17 days to 10. It also ends same-day registration, requiring voters to register, update their address or make any other needed changes at least 25 days ahead of an election. A high school civics program that registers tens of thousands of students to vote each year in advance of their 18th birthdays has been eliminated.
A provision also would end straight-ticket voting, in place in the state since 1925.
Critics said disclosure requirements intended to make clear who is underwriting campaign ads also would be weakened, and note that political parties would be allowed to take in unlimited corporate donations. The cap on individual campaign donations also would rise from $4,000 to $5,000.
McCrory, who announced the signing in a statement, appeared in a 95-second message on YouTube giving his reasons and focusing solely on the voter identification component.
The first-term governor cited laws that require people to present photo IDs to board airplanes, cash a check or apply for government benefits. "Our right to vote deserves similar protection," McCrory said in the video.
The governor's video message also took aim at opponents.
"Many of those from the extreme left who have been criticizing photo ID are using scare tactics," McCrory said. "They're more interested in divisive politics than ensuring that no one's vote is disenfranchised by fraudulent ballots."
McCrory, a former Charlotte mayor who ran as a moderate but now shares power with conservatives who control the state legislature, also assailed critics when he recently signed a measure containing new abortion restrictions that had been attacked by Democrats and abortion rights groups.
Democratic Attorney General Roy Cooper, a Democrat, was among those who had urged a veto.
"This bill was much more than just voter ID," Cooper said in a statement Monday. "There were dozens of reasons to veto this bad elections bill with its restrictions on voting, more corporate campaign money and reduced public disclosure being just a few."
Although records show only a handful of documented cases of in-person voter fraud that were prosecuted in the last decade, Republicans compared North Carolina's elections to the tainted races in Chicago in the 1960s. Meanwhile, Democrats and other opponents predicted the changes -- if implemented -- would lead to long lines and chaos at the polls, as was the case in 2012 after early-voting days were cut in Florida.
Charlotte correspondent Mitch Weiss contributed to this report.
Copyright 2013 The Associated Press.