His passport was siezed by the FBI and he was told he wouldn't be let back into the US if he left.
So he performed at the Peace Arch, for both country's peoples:
http://www.caw.ca/whatwedo/humanrights/robeson.aspFrom People's Voice, December 1-31, 2001 (not on-line):
The 1952 Concert
The venue was an odd one for one of the great artists of the 20th century, and the sponsor, the International Union of Mine, Mill, and Smelter Workers equally curious, or maybe not. "Mine Mill", as it was known, had been founded in a jail cell in Idaho in 1893. It was a union that represented some of the most militant North American workers, the hard rock miners, whose battles with the mine owners were legendary.
Paul Robeson, whose own uncompromising militancy in the face of oppression and injustice was equally well known, had been invited to sing at the Fourth Canadian Convention of the union in Vancouver in February of 1952. The American authorities, however, had seized Robeson's passport, and he was denied permission to leave his country. The convention heard Robeson sing over the telephone and promised to organize a concert on the US-Canadian border, and indeed they did.
Accompanied by Lawrence Brown on piano, Robeson sang and spoke for 45 minutes. He introduced his first song stating "I stand here today under great stress because I dare, as do you -- all of you, to fight for peace and for a decent life for all men, women and children". He proceeded to sing spirituals, folk songs, labour songs, and a passionate version of Old Man River, written for him in the 20's, slowly enunciating "show a little grit and you land in jail", underlining the fact that his government had turned the entire country into a prison for Robeson and many others.
It was a magnificent performance and a triumph for a movement facing the scourge of McCarthyism and the Red Scare. The Korean War was at its height, Ethel and Julius Rosenberg were under sentence of death, and it seemed the social and political gains of the previous generation were being eroded by a right-wing offensive. The Peace Arch Concert was a rare victory, a massive solidarity, and a demonstration that the dream of a different world was still alive. The concert was recorded and issued as a record by the union.