More than 800 trade unionists have been killed in Colombia over the past six years, by government count, yet the number of those slayings solved can be counted on one hand.

Union organizing can be a deadly activity anywhere but is particularly dangerous in Colombia, where decades of political violence and lawlessness compel some unscrupulous employers to hire assassins.

"There's almost total impunity," says Flavio Arias, vice president of the CUT labor umbrella organization, which represents Colombia's 530,000 unionized workers.

Now Colombia's reputation as the deadliest place in the world to be a labor organizer threatens to sink one of President Alvaro Uribe's proudest achievements: a free-trade agreement with President Bush, who is expected to use his visit to Colombia on Sunday to press for congressional approval.

The union-friendly Democrats who now control the U.S. Congress are so concerned about the unsolved labor killings that they are threatening to derail the trade pact entirely unless Uribe makes clear progress.

On Tuesday, Bush acknowledged he faces a tough fight getting the plan through Congress, but said he would strongly defend it. "It's going to be a battle, he said in Washington.

In a speech last May Day -- the international day of the worker -- Uribe boasted of "working with complete devotion so that one day we can stand before the world and say not a single trade unionist has been killed in Colombia."

Yet the number of slain unionists rose last year even as the homicide rate dropped under Uribe's law-and-order government. The Labor Ministry says 43 trade unionists were killed in 2005, and 58 last year.

None of those slayings have been solved.
"Colombia's labor record is one of most problematic and controversial of any countries to sign a free-trade agreement," said Thea Lee, policy director of the AFL-CIO, in Washington.

The biggest threat is hitmen hired by employers, especially in parts of the country where many workers toil in semi-feudal conditions and illegal militias hold sway.

That is the allegation in the 2001 killings of three mining union leaders in a case involving a U.S. coal company's Colombian arm.

A federal judge in Alabama on Monday ruled that a civil suit could go to trial against Birmingham-based Drummond Co. Inc., whose local president is alleged to have played a role in the killings.

The suit says two union leaders were taken off a Drummond bus and shot to death by assassins hired by the company while a replacement union leader was also gunned down by paramilitaries.

Colombia's union membership rate, at about 5 percent, is one of Latin America's lowest, and the chief federal prosecutor's office has a backlog of 1,300 cases of killings, threats and intimidation involving trade unionists.

"It's an embarrassment how slow we've been to take on these cases," said the chief of the office's human rights division, Leonardo Cabana. He's got just 13 prosecutors nationwide tackling the labor caseload.

Among the victims is Jorge Abril Parra, who was shot twice in the head last year on his way to work at Tapas La Libertad, a metal caps and bottling plant owned by one of Colombia's biggest conglomerates.

Parra had survived a previous attempt on his life, but the company ignored requests from the Sintraime metal workers' union that he be transferred, said union president Felix Herrera.

A few months after Parra's slaying, 25 frightened co-workers -- all union members -- accepted a company retirement offer.

Although there is no evidence linking Parra's employer to his slaying, Herrera said that "there's no doubt the company took advantage of his death to defeat the union." A spokeswoman for Tapas La Libertad did not return repeated phone calls seeking comment.

Often, the hostility toward unions comes from the top.
Jorge Sanchez, vice minister of labor, told The Associated Press that unions inflate the numbers of slain members "because they thrive on violence and blood."

Protecting labor leaders does appear to be a government priority, however. Guarding them -- with bulletproof vests or bodyguards -- consumes 40 percent of a nearly $20 million security program for human rights activists, journalists and other threatened individuals.

But labor unions, and their Democratic allies, demand more.
"Countless numbers of trade unionists in Colombia have been intimidated, have been threatened and have been murdered," said U.S. Rep. James McGovern, a Massachusetts Democrat who visited Colombia last week.

"Until those issues are addressed, I think there's going to be some rough sledding for the trade agreement."
U.S. Rep. Charles Rangel of New York, powerful new chairman of the House Ways and Means Committee, would not back the trade deal despite a lobbying trip by Uribe in November.

Nor would U.S. Rep. Gregory Meeks, also of New York: "I don't think the free-trade deal with Colombia will be approved in its current form."