Three men with links to a Canadian mining company have been charged in the killing of a Mexican activist, threatening already strained relations between the countries on the eve of a visit to the same region by Governor-General Michaelle Jean.

A spokesman for Calgary-based Blackfire Exploration Ltd. confirmed that an employee, a former employee and a one-time company contractor were arrested in the Nov. 27 murder of Mariano Abarca Robledo, who had led local opposition against Blackfire’s barite mine in Chicomuselo, Chiapas.

Ms. Jean is preparing to travel to Chiapas Tuesday for a dinner with the state’s governor. Tensions are already high between the two countries over visa restrictions placed on Mexican visitors by the Canadian government in July.

The arrests come at a critical time for Canada’s relations with a key trading partner, as well as the reputation of Canada’s mining industry abroad.

Canada’s miners are lobbying against a private member’s bill that would impose sanctions on resource companies found to have committed human rights and environmental abuses in other countries. The government, including Peter Kent, the junior foreign minister for the Americas who is accompanying the Governor-General in Mexico, voted against Bill C-300 during its second reading in April.

The slain activist, Mr. Abarca, was a leader in an organization called Mexican Network of People Affected by Mining (REMA), that had publicly protested Blackfire’s mine and made allegations that the operation was damaging the environment and contaminating a nearby river. He was gunned down in a drive-by shooting outside his home by a motorcyclist.

Caralampio Lopez Vazquez, who currently works as an operator and a shift supervisor at the mine, is among the three men facing charges in the killing.

“One of them is currently an employee and we are working with authorities to see how things will proceed,” Blackfire spokesman Alonso Cedeno said in a telephone interview from Chiapas.

Mr. Cedeno said the company is offering full co-operation to the police and had no involvement in the crime or the reported threats made against Mr. Abarca before his death.

Hearings into Bill C-300 have put a spotlight on the conduct of Canadian mining companies operating overseas and led to sensational allegations – of physical violence and environmental devastation – against some of the country’s largest mining firms.

The Blackfire miner’s arrest is sure to provide fodder for those who believe that Canadian mining firms operating in developing countries need more regulations.

“I expect some people will exploit this for their own purposes,” said Robert Wisner, a lawyer with McMillan LLP, who testified against the bill on behalf of the mining industry.

“The fact that the Mexican authorities have acted proves that Mexico can enforce its own laws,” he added.

There are well over 230 Canadian mining companies active in Mexico. About 200 are involved in exploration, and about 40 are running mines that are producing gold, silver, lead and other minerals including barite, which is used in oil and gas exploration.

Protests over the shooting death of Mr. Abarca were already expected to greet the Governor-General, but she now faces increased rancour with the criminal allegations involving a mine employee.

Ms. Jean, accompanied by Mr. Kent, is to arrive in Tuxtla Gutierrez Tuesday for a dinner with Chiapas Governor Juan Jose Sabines.

Tomorrow, she will visit the city of San Cristobal de Las Casas, a forest-encircled Chiapas city where the official program includes a dramatic presentation based on the themes of indigenous rights, cultural survival, and ecology – before a meeting about Canadian-funded aid programs in the region.

The Governor-General’s spokesman, Marie-Eve Letourneau, said there were no plans to change Ms. Jean’s trip.

A spokesman for the Mexican embassy in Ottawa, Alberto Lozano, said he had no details other than those released by state authorities.

“We are aware of the crime. We regret the death of Mr. Mariano Abarca Robledo. The case is under investigation by local authorities in the state of Chiapas,” Mr. Losano said.

There have been tensions between Mexico and Canada since Ottawa slapped visa requirements on Mexican visitors in July, arguing that too many were claiming refugee status after they arrived here.

One Mexican Senator, Rosario Green Macias, called the process “humiliating,” saying the process she had to endure – bringing a half-dozen bank statements, proof she owned property and a letter from the Senate confirming her position – went too far.

During a visit to Mexico in August, Prime Minister Stephen Harper blamed the visa flap on Canada’s dysfunctional refugee system. The Governor-General and Mr. Kent were supposed to be trying to renew the friendship between the two nations on this trip.

Mr. Kent’s spokesman, said in an e-mail from Mexico last night that the two countries have a “broad” relationship, and the trip has been “extremely positive thus far.”

“There will be no changes to our itinerary and we look forward to a busy few days here before advancing to Guatemala,” she said. “We are aware of the situation in Chiapas and were saddened to hear of the death of Mr. Abarca. We understand that there is an ongoing Mexican investigation and not much more can be said at this point.”

Blackfire is a privately held company that, in addition to operating the barite mine in Mexico, is also developing mining projects in British Columbia. Officials at the company’s headquarters in Calgary directed all enquiries to the company’s spokesman in Mexico.