President Donald Trump’s executive order denying U.S. citizenship to the children of parents living in the country illegally has faced the first of what will be many legal tests.

A federal judge temporarily blocked President Trump’s executive order that aims to restrict automatic citizenship to babies born on U.S. soil, calling it “blatantly unconstitutional.” The order Mr. Trump signed on Monday was an effort to upend the nation’s immigration laws and reverse decades of precedent and would affect children born to undocumented or temporary immigrants.