Federal investigators are examining family text messages obtained from a phone belonging to Representative Ilhan Omar’s sister as part of an ongoing inquiry into allegations of immigration fraud, sources familiar with the case said last week. The device, reportedly seized earlier this year, is believed to contain evidence that led to a search of Ms. Omar’s Washington-area residence last Monday by homeland security agents.

Officials spent several hours at the congresswoman’s home and removed multiple boxes of materials. The investigation, which is before a federal grand jury in Minnesota, centers on whether Ms. Omar and her family provided false or misleading information in immigration documents submitted after they fled Somalia’s civil war and were admitted as refugees in the 1990s.

Federal subpoenas have recently been issued to Ms. Omar’s sister Sahra Noor, a health care executive and author, as well as others close to the congresswoman. The Justice Department has not commented on specifics regarding the phone seizure or the timing and location of the device’s confiscation.

The search of Ms. Omar’s residence drew condemnation from Democratic lawmakers, in part because it appeared to violate a Justice Department policy discouraging overt investigative actions close to an election that might influence its outcome. Ms. Omar, who represents a district encompassing Minneapolis, is seeking a fifth term in next month’s midterm elections. The congresswoman’s campaign has reported a surge in donations nationwide since the search.

The inquiry also involves questions about Ms. Omar’s age when she acquired U.S. citizenship through her father’s naturalization process. While Ms. Omar has stated she naturalized before turning 18, officials have suggested she might have been an adult at the time, which would affect her eligibility to derive citizenship through a parent.

Homeland Security Secretary Markwayne Mullin has asserted that the government is building a “strong case” against Ms. Omar, indicating potential legal consequences including deportation. Vice President JD Vance has publicly stated his belief that Ms. Omar committed immigration fraud and emphasized holding her accountable.

Ms. Omar’s legal team has condemned the search as unjustified and unconstitutional, emphasizing the congresswoman’s protections under the law. Lawyers Amy Jeffress and Joshua Matz contended that the Justice Department did not comply with conditions ordered by the presiding judge, including notifying Ms. Omar of her congressional immunity and obtaining her consent to the search. They also said investigators delayed her access to counsel, which they argue violated her constitutional rights.

The Justice Department responded by asserting that its personnel adhered to the parameters established by the judge and described the lawyers’ letter as “riddled with false allegations and inaccuracies.”

Ms. Omar and her supporters say the investigation is politically motivated and part of a prolonged campaign of harassment. In a recent fundraising email, she described the investigation as more than “racist rhetoric” and accused the Trump administration of attempting to strip her of citizenship. Former President Donald Trump has been a vocal critic of Ms. Omar, often targeting her and Minnesota’s Somali community.

This is not Ms. Omar’s first brush with federal investigations; previous inquiries into her finances and campaign activities have not resulted in charges. The current case comes amid heightened political tensions as the midterm elections approach.