People Before Profit TD Richard Boyd Barrett made the decision of the Taoiseach to welcome Donald Trump as "shameful" in Ireland.
He says he has already contacted other groups to organize big demonstrations when the US president arrives in November.
He says his politics have made the world more dangerous and divided.
Deputy Boyd Barrett says he does not like what Mr. Trump stands for.
"Donald Trump is a promoter of the politics of hatred, of greed, of war and of prejudice and I find it really shameful that Leo Varadkar would bring him here to legitimize and empower that policy.
"I really want people who believe in peace, equality and justice to come out and protest against Trump's really bad political agenda."