Zimbabwe deported a South African trade union delegation on Tuesday after it arrived on a fact-finding trip despite orders from President Robert Mugabe's government to stay away.
Irate members of the 13-strong team from the Congress of South African Trade Unions (COSATU) raised their fists in protest and chanted liberation slogans as they were marched through Harare airport, witnesses said.
A spokesman for COSATU - a key ally of South African President Thabo Mbeki's ruling African National Congress - deplored the group's expulsion.
"The deportation of a peaceful, fact-finding mission is a totally unacceptable attack on basic human rights," COSATU spokesman Patrick Craven said in Johannesburg.
Zimbabwe immigration and government officials were not immediately available for comment. South African Foreign Ministry spokesman Ronnie Mamoepa said the government was aware of the deportation.
"Our diplomatic mission has informed us of this. They continue to monitor the situation," Mamoepa said.
The COSATU delegation arrived in Harare on Monday on what it described as a mission aimed at helping Zimbabwe resolve its political and economic crisis.
The trip was made in defiance of a letter from Mugabe's government saying the mission was "not acceptable".
The South Africans were detained at Harare's main airport for nearly an hour on Monday while authorities sought to ban them from meeting some rights groups like the National Constitutional Assembly which has organised several anti-Mugabe protests in recent years.
COSATU said the group refused to accept restrictions on its activities in Zimbabwe.
Its deportation marks a fresh challenge for South Africa's Mbeki, who has been frequently criticised for failing to take a tough enough stance on developments in Zimbabwe.
"We are going to launch an international campaign of protest," he said.