On the eve of President Obama’s visit to Mexico, a possible major confrontation is brewing between the Mexican Mine and Metal Workers Union and the conservative, pro-business government of President Felipe Calderon.

Since Monday, April 13, miners and their allies have been blockading the port of Lazaro Cardenas on Mexico’s west coast to protest a union-busting ruling by a labor tribunal on a strike at the giant Cananea copper mine in the Western state of Sonora. The miners say they have stopped more than 2,000 containers from being loaded onto ships in the port. But the latest news is that hundreds of troopers of the feared Federal Preventive Police (PFP in Spanish) may be on their way to stop the blockade. As of this morning, 400 federal police have shown up in Cananea.

The fight between the Mine and Metal Workers Union and the right-wing governments of presidents Fox and Calderon of the National Action Party (PAN) has been going on for several years, since the union’s leader, Napoleon Gomez Urrutia, broke with the old pattern in Mexico of traditional unions negotiating wage increases with both the management and the government. He won higher wages for his members than otherwise would have been the case. The Fox government then cooked up an accusation of corruption in management of a union trusteeship against Gomez and his associates, which drove him into exile in Vancouver, Canada, where he remains. Now a criminal court in Mexico has declared Gomez to be innocent of the charges but the government is still trying to have him extradited from Canada.

Meanwhile, a strike broke out in the Cananea mine, which belongs to U.S.-based Southern Copper, an affiliate of the Grupo Mexico transnational whose CEO is Calderon ally German Larrea. The union says that the strike is about dangerous and unhealthy conditions in the mine, but the management and the government, acting in more and more obvious collusion, claim that if Gomez Urrutia were not the head of the union, the strike would have been settled long ago.

Following another tack, the government has been trying repeatedly to get Gomez removed as union leader. In January of last year, the government-influenced National Tribunal of Arbitration and Conciliation declared the strike to be “non-existent” and the government apparently sent in armed security personnel who took over the mine with some violence. The union then got a labor court to reverse the decision, but though the court declared the strike to be legal, it refused to order the government to return control of the facility to the union.

On Tuesday, as had been expected, the Federal Board of Arbitration and Conciliation authorized a proposal by the Grupo Mexico management to close the Cananea mine and fire all 1,200 unionized workers, under the pretext that the occupation of the mine by strikers has led to so much damage to the machinery that the mine can’t operate. The strong implication of this move is that the company will reopen the mine later with workers not affiliated with the National Mine and Metal Workers Union. In response, the miners’ took journalists on a tour of the mine in which they showed that the machinery is operative.

This move by the government arbitration panel, obviously pushed by both the Calderon government and the Grupo Mexico management, was what caused the union to organize the blockade of the port of Lazaro Cardenas as a protest measure.

From his Canadian exile, miners’ leader Gomez Urrutia issued a statement to the press in which he denounced the arbitration board’s decision as unconstitutional and added, “We are in the struggle and we ask and propose to you once more to close ranks based on our values and principles as workers, of our unity and loyalty, with regard to the right to strike and union autonomy and freedom” (La Jornada April 14).

Meanwhile, the main left-wing opposition party in the Mexican Congress, the Revolutionary Democratic Party, has announced that when President Obama is in Mexico, they will ask him to begin the process of reopening negotiations on NAFTA, especially its agricultural clauses.

Obama and U.S. labor unions have complained for their part that there are not enough protections for workers in NAFTA. The potential spectacle of heavily armed police assaulting mine workers and their allies, in the context of a dispute which boils down to a joint government-management effort to break a strike and remove the legally elected leadership of a union, may play into that dynamic in interesting ways.