WASHINGTON-Congress should delay voting on a free-trade agreement with Colombia until President Alvaro Uribe proves he is serious about reducing violence and jailing murderers of trade unionists, congressional opponents of the deal said on Thursday.

The demand came as Uribe was making his second visit to Washington in five weeks to lobby for approval of the pact and reassure Democrats who want to redirect and reduce U.S. anti-drug and military aid Colombia relies on to fight guerrillas and cocaine.

"Mr. Uribe has come back to Washington too soon. Come back next year, Mr. Uribe, and let's see what has actually been accomplished," said Rep. Jan Schakowsky, an Illinois Democrat who joined other lawmakers, human rights and labor groups at a news conference to protest the proposed pact.

Uribe has led a hard-line campaign to combat left-wing rebels and disarm illegal paramilitary gangs with the aid of billions of dollars in military and counter-narcotics assistance from Washington.

Violence has dropped sharply and foreign investment is flowing into the economy. But a probe into paramilitary links to politicians has led to the arrest of pro-Uribe lawmakers and a slew of investigations.

Uribe says that proves Colombia's justice system is working. He has also pushed for more investigations into labor union killings and for more funds for the judicial system.

But Rep. Phil Hare, an Illinois Democrat and former union leader, said violence against Colombian trade unionists remains too high and two few perpetrators are brought to justice.

"Twenty-one hundred labor leaders have been murdered in Colombia since 1991. There have been only 37 convictions," Hare said. "If I had been born in Colombia, there is a strong possibility ... I could be dead."

TIMING UNCERTAIN

Colombia should be required to show progress in reducing violence and bringing murderers to justice "over at least a two-year period" before U.S. lawmakers vote on the pact, said Rep. Linda Sanchez, a California Democrat.

Last month, the Bush administration struck a deal with congressional Democrats to include a commitment to abide by core international labor standards into the Colombia agreement, as well as other pacts with Peru, Panama and South Korea.

But senior Democrats also have insisted Colombia take additional steps to address concerns about anti-labor union violence and the related paramilitary scandal that has ensnared members of Uribe's own party.

House of Representatives Ways and Means Committee Charles Rangel, a New York Democrat who was to meet with Uribe on Thursday, told Reuters the timing of a vote on the Colombian agreement was still unclear.

"We're working with the State Department, the Treasury and USSR (U.S. Trade Representative's Office) on conditions where people might be in position to support it," said Rangel, whose committee has initial jurisdiction over trade agreements.

In a sign of the increased scrutiny Colombia faces, a House appropriations subcommittee on Tuesday proposed cutting its 2008 aid budget by 10 percent to $530 million.

The panel trimmed the military and drugs component of the package from 76 percent to 55 percent, and bumped up the social and development part to 45 percent from 24 percent.