Senate Republicans on Thursday boycotted a hearing on three pending free-trade agreements, delaying action on a centerpiece of the Obama administration’s effort to boost U.S. exports.

Republicans object to a worker assistance program the administration wants to include as part of a free-trade agreement with South Korea. The Trade Adjustment Assistance program costs about $1 billion and has drawn bipartisan support in the past.

But in the charged environment over spending and debt negotiations, the dispute is complicating what the administration had hoped would be an easy push to broaden trade with South Korea, Colombia and Panama.

Senate Finance Committee Chairman Max Baucus (D-Mont.) called a meeting of his panel at the Capitol at 3 p.m. Thursday, but the 11 Republicans on the committee failed to show up.

Five of those Republicans, led by Sen. Orrin G. Hatch (R-Utah), were instead holding their own news conference, at which they slammed Democrats for the “obnoxious” move of scheduling the markup late on a Thursday afternoon — which Republicans argued would hinder the panel’s consideration of the nearly 100 amendments to the trade pacts that had been submitted — and for attaching a renewal of the trade adjustment program to the South Korea deal.

“The president knew where we stood, and he decided to ignore those who don’t agree with him,” Hatch said.

The day’s events show how complicated the politics of trade remain for the Obama administration.

U.S. Trade Representative Ron Kirk was able to negotiate significant changes in the South Korea pact that made it palatable to corporate and union interests who had opposed it, and he lobbied the government of Colombia to make more tangible progress in protecting labor activists from violence.

But the agreements remain, at some level, polarizing in a way that the administration has not been able to resolve. A compromise agreement announced this week looks less certain. Some leading Democrats don’t like the Colombia deal, because of the country’s long reputation for anti-union violence. Republicans don’t like the South Korea deal enough to let it pass with the trade adjustment program as part of it.

The standoff led to the odd spectacle of Democratic members of the Senate Finance Committee gathered on their side of a half-empty committee table, greeted by a phalanx of vacant chairs on the Republican side. They extolled the benefits of free trade, talked of the need to generate jobs at a time of high unemployment and wondered about the GOP no-show.

“We had an option today to strengthen our economy, and our Republican colleagues refused to show up for work,” said Sen. Kent Conrad (D-N.D.). “Hundreds of millions of people showed up for work today, and they expected we would show up to solve our country’s problems.”

The delay is a disappointment for the administration and its newfound ally on the issue — the U.S. Chamber of Commerce. In a letter to the Finance Committee, Chamber lobbyist R. Bruce Josten said the group supported not just the free-trade agreements but the trade adjustment program and the other items being tucked into them.

He urged senators to sign off on the agreements and — in italics — “to oppose all amendments.

From the business community’s perspective, time is running short. Europe has a free-trade pact with South Korea that begins Friday, and Canada has one with Colombia as of Aug. 15.

There is a widely held assumption that if the agreements are not approved before the summer recess, the politics of the upcoming election year will make them harder to move.