* Workers may vote for walkout or send dispute to arbitration * Strike vote to conclude on January 29 - union By Jack Kimball BOGOTA, Jan 22 (Reuters) - Workers for Colombia's largest coal exporter, Cerrejon, will decide whether to go on strike or send a wage dispute to an arbitration committee on January 29. Negotiations at Cerrejon are the first in a series of labor talks this year in the world's fourth-largest exporter of the material whose mining and oil companies have suffered in recent years from increased labor unrest and a rise in rebel attacks. "Workers are determined to vote for a strike," Orlando Cuello, board member of the Sintracarbon union, told Reuters. Laborers at the mine started voting on Tuesday while port workers began on Monday afternoon, and the process is supposed to end on January 29, the union said. If laborers vote for a walkout, under Colombian law, they cannot leave their posts on the first day after the vote or the last day during a ten-day window they have to start it. Workers could also decide to send the dispute to an arbitration committee. Cerrejon has around 4,500 unionized laborers, according to the company. Unions often use the threat of a strike to pressure companies into better deals for workers. Juan Carlos Restrepo, Cerrejon's vice-president of public affairs, said that a strike would be "a disaster for everyone". "We're always open to a deal ... we hope that the other side is too," he told Reuters. Cerrejon offered a 5 percent wage increase in the first year of the contract while the union was seeking 7 percent, according to union and company officials. In 2011, laborers at Cerrejon voted to strike but reached a deal with the company before actually walking off the job. Cerrejon - a joint venture between BHP Billiton, Anglo American and Xstrata - produced 34.6 million tonnes of coal last year, 4 percent more than expected. It exported 32.8 million tonnes, 2.5 percent above its goal. The company is investing $1.3 billion to boost annual production to 40 million tonnes by 2015. Workers at U.S. coal miner Drummond's operations in Colombia are expected to negotiate later this year after reaching a three-year deal in 2010 to avoid a strike over pay and bonuses at the nation's second largest coal exporter. In Colombia, more than a decade of U.S.-backed strikes against leftist rebels and drug lords have attracted billions of dollars in investment mainly into the oil and mining sectors. The flood of investors has presented the government with a new host of challenges including institutional strains and growing demands from environmental and social groups. Security is still a concern though. On Monday night, guerrillas threw a bomb onto Cerrejon's railway in the Guajira province, according to military sources. The company said there had been no injuries or fatalities in the attack and that the train was operating normally.