Children are waiting months for visas or being rejected because of the current rules.
Labour peer and former child refugee tells HuffPost UK the home secretary's plans are "driven by politics, not by a wish to have a sensible policy".
"The only winners if we remove legal routes to safety for refugee children trying to reach family here are the criminals and the traffickers," says Lord Dubs.
Exclusive: Twelve councils write to the prime minister ahead of crunch Lords vote on family reunion for lone child refugees after Brexit.
The Labour peer, who came to the UK as a child refugee fleeing the Nazis, tells HuffPost UK he is "worried" family reunion rules could be tightened after Brexit.
'I will keep fighting and so many other people will keep fighting to protect those children who need it the most.'
Campaigners want programme re-opened after Government miscount.
Just 350 children were accepted into the UK out of the 3,000 expected.
Refugees as young as eight left 'bewildered' by inaction.
Lord Dubs to withdraw amendment after victory