Five Muslim US residents sued the federal government on Thursday, accusing the Department of Homeland Security for unfairly causing delays in their permanent residency and citizenship requests.

The plaintiffs include Palestinian Muslims Ahmad and Reem Muhanna, who had applied for US citizenship in 2007 and had their applications rejected in 2012. Others include Ahmed Hassan, a Muslim refugee from Somalia who has been seeking permanent residency since 2006, and Iranians Neda Behmanesh and Abrahim Mosavi.

The plaintiffs claim that their immigration petitions were unfairly stalled and flagged for potential national security concerns, reported Reuters.

The criteria laid out for flagging applications under the Controlled Application Review and Resolution Program (CARRP) are secretive and broader than authorized by the US Congress, the immigrants claimed.

Representing the immigrants in the federal court in Los Angeles was Jennie Pasquarella, an attorney with the American Civil Liberties Union (ACLU) of Southern California.

"Our clients are long-time, law-abiding residents of the United States who, for years, the government has walled off from becoming citizens and lawful residents of this country without legal authority to do so," said Pasquarella in a statement.

"Under this unfair and unconstitutional program, the government has blacklisted their applications without telling them why and barred them from upgrading their immigration status in violation of the immigration laws."

The ACLU claims that the immigrants are among thousands of US residents of Arab, Middle Eastern, Muslim or South Asian backgrounds who are denied citizenship and green cards without fair reasoning.

The US Constitution mandates giving residents the ability to contest the immigration decisions made by authorities.

"Very much like the no-fly list, people are not told that they're subject to CARRP, that they've been labelled a national security concern, and that they're held up for that process," said Pasquarella. "They must be told why, and given an opportunity to respond."

A US Citizenship and Immigration Services spokesperson declined to comment on the lawsuit, but said the CARRP system aims to give immigration officers the flexibility to manage a variety of cases, according to Reuters.