U-S corporate giant-- Walmart-- is escalating its retaliatory measures against employees who speak out against the company's tactics. Workers say they’re being fired for criticizing the firm or demanding changes in workplace conditions. Now, workers have filed federal charges against Walmart to stop its high-handedness.Peoples working in Walmart stores and warehouses have spent the past year demanding improvements in work conditions from America’s largest multinational corporation. Workers have already staged walkouts, strikes and protests to highlight what they say the illegal tactics of Walmart to control the global supply chain. Now, workers complain that the retail giant is striking back. Workers say Walmart is retaliating against them for speaking out about work conditions at the company’s warehouses. Javier Rodriguez says he was fired from his job at a Walmart-contracted warehouse for being an outspoken employee. Rodriguez says he attempted to contact the company to do the right thing for employee safety. But he says Walmart looks the other way when workers are abused. Walmart officials did not return a call for comment. Labor leaders say Rodriguez is just one example of how Walmart handles calls for change. They say, over the past year, the company has increased its use of intimidation in order to silence workers. That’s why Rodriguez has filed federal charges to protest what he says an illegal firing. Labor leaders are now pushing for other fired workers to file charges as well. Walmart is also under increased scrutiny after denying a chance to visit the site of a fatal fire at a garment factory in Bangladesh. Several U.S. and European politicians plus representatives from other large retailers took part but Walmart did not take any heed to the tragedy.