More than 30 members of Congress will boycott Donald Trump's inauguration on Friday, amid escalating outrage over alleged connections between the president-elect's team and Russia and disparaging remarks about civil rights veteran John Lewis. As the US marked its national holiday honoring Martin Luther King Jr on Monday, the number of Democrats pledging to shun Friday's ceremony and celebrations rose. Keith Ellison, the first Muslim elected to Congress and a candidate for chair of the Democratic National Committee, joined them. Their extraordinary step was praised by progressive leaders. A little before 1pm, however, Martin Luther King III, the oldest child of Martin Luther King Jr, arrived at Trump Tower in New York to meet the president-elect. Around 50 minutes later, King emerged from the building's elevators and spoke to reporters. Asked why he had met Trump, who did not talk to the press but was seen shaking his guest's hand, he said it was a constructive meeting and added: "We have got to move forward." King and William Wachtel, a New York lawyer, said they spoke to Trump about voter participation and how to carry forward King's father's legacy by making it "easier for everyone to vote". "President-elect Trump has committed to working with us," Wachtel said. In 2013, a supreme court decision struck down key elements of the 1965 Voting Rights Act, a central achievement of the civil rights movement designed to protect minority voters. In 2013, a supreme court decision struck down key elements of the 1965 Voting Rights Act, a central achievement of the civil rights movement designed to protect minority voters. Asked about Lewis, King said: "Things get said on both sides in the heat of emotion. And at some point in this nation we've got to move forward." He added that he would "continue to evaluate" Trump's commitment to representing all Americans. "I believe we have to consistently engage with pressure, public pressure," King said. "It doesn't happen automatically, my father and his team understood that, did that. "I think my father would be very concerned about the 50 to 60 million people living in poverty. It's insanity that we have poor people in this nation, it's unacceptable. We need to be talking about how to clothe people, how do we feed people." One civil rights veteran told the Guardian she supported the Trump-King meeting but also praised members of Congress who plan to boycott the inauguration. "Those members of Congress feel that not attending the inauguration is making a statement that they are against the politics put forth by Donald Trump," Doris Crenshaw, who campaigned with Rosa Parks and met Martin Luther King Jr before his assassination in 1968, told the Guardian. She called on Trump to call Lewis and "have a conversation". Cornell William Brooks, president of the National Association for the Advancement of Colored People (NAACP), has demanded that Trump apologize to Lewis, the long-time Georgia congressman who had his skull broken by the police during the pivotal Selma to Montgomery march of 1965. Lewis said last week he would not attend the inauguration and did not regard Trump as a legitimate president, following intelligence reports of Russian interference in the election. Trump launched a fierce counterattack on Twitter in which he accused Lewis of being "all talk" and warned him to focus on his district which was "crime infested".