Eight civil rights groups have condemned President Donald Trump’s expansion of his travel ban to six majority-Muslim African countries, calling the move racist and unconstitutional.

“The expanded Muslim Ban is another attack on the rights, the dignity and the identity of Black communities,” the groups, including the NAACP, Color of Change and the National Action Network, said in a statement.

The expansion, which was announced Jan. 31, adds Nigeria, Sudan, Tanzania and Eritrea to the travel ban and maintains the ban on travel from Libya and Somalia. Together, these countries account for over a quarter of the population of Africa. Myanmar and Kyrgyzstan will also be added to the ban, the only non-African countries included. Civil rights leaders say the ban takes effect this week and they will be researching legal methods to try to block the ban in the days ahead.

President Donald Trump said he signed the proclamation because of national security concerns, claiming the countries had not met minimum security standards.

“We’re adding a couple of countries to it,” Trump told reporters last month. “Our country has to be safe. So we have a very strong travel ban and we’ll be adding a few countries to it.”

Some in Nigeria, Africa’s most populous nation, have expressed outrage while the government issued a brief statement saying it would study the U.S. requirements.

Hilary Shelton, the NAACP’s senior vice president for advocacy and policy and the director of its Washington bureau, said that there is no real national security justification for the travel ban and that the expansion is motivated by racism.

“By no means should the American people, with our history and commitment to freedom and justice for all, allow such a discriminatory policy to be implemented under our name,” Shelton told NBC News. “It is wrong, it is misguided and, quite frankly, it is sadly racist.”

Scott Simpson, public advocacy director for the civil rights organization Muslim Advocates, agreed. He said the ban is an attempt to prevent more black and brown people from immigrating to the U.S.

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“I think it's certainly hard to ignore the fact that this is a ban on black immigration,” Simpson said in an interview. “The administration wants to keep America as white as it can possibly keep it, and it wants to treat people of color with cruelty and discrimination and make their lives harder.”

The ban, unlike the more sweeping restrictions on travel from countries like Iran, will not apply to nonimmigrant visas typically issued to students, tourists and visitors. Instead, it targets those with immigrant visas, and it prevents immigrants from Sudan and Tanzania from participating in the diversity visa program, which awards green cards to immigrants through a lottery system.

Civil rights advocates predict that despite the ban’s focus on immigrant visas, it will be more difficult for immigrants’ family members, students, and others with temporary visas to travel to the country as well.

“Whenever you move to implement anything as broad and pervasive as a policy like this, an awful lot of innocent people end up being caught up in the system, held up, detained and otherwise having problems,” Shelton said.

Some immigrant communities in the U.S -- both African and from the countries included in the expansion -- fear that the ban will make visiting and reuniting with family living on the continuent much more difficult.

“We have families that we work with weekly, monthly, that are American citizens, people who were born in the United States, whose family is separated because of the ban,” Simpson said. “Now, anyone who has family who are Nigerian, Sudanese, Tanzanian, they are also going to be subject to that deprivation.”

Eritrea’s information ministry asserted the U.S. decision was made “without justification to send a negative signal” and runs counter to U.S. policy of constructive engagement.

Trump has called Haiti and African nations “shithole countries,” which Shelton said betrayed a general pattern of bigotry and ignorance behind discriminatory policies like the travel ban.

“I think many of us remember the kind of language that was being utilized by the president as he referred to these countries, to their people, and how insulting that was,” Shelton said. “Now he's moved that one step further.”

For Simpson, the travel ban expansion is yet another in a long line of xenophobic and racist positions by Trump, who Simpson said had based his political career on the marginalization of nonwhite people.

“Trump's political career started with birtherism, this idea that a black American president certainly doesn't count as American,” he said. “His portrayal of blackness, of Muslims, of being Latino, is as something that's inherently foreign.”

There has been legal and political pushback on the travel ban since Trump announced its first iteration in March 2017. On Feb. 12, the House Judiciary Committee voted to advance a bill to terminate Trump’s travel ban completely, though it’s unlikely to pass the Republican-led Senate. And after initially being upheld by the Supreme Court in a 5-4 ruling in 2018, a federal appeals court heard another legal challenge to the ban in January.

According to Shelton, the NAACP and other civil rights-focused legal groups are preparing to challenge the expansion in court.

“Our lawyers and others are meeting and looking for the most effective approaches to push back on this,” he said.

The Associated Press contributed reporting.