For auto parts manufacturers in the Mexican state of Nuevo Leon, the fine print of a Pacific trade deal negotiators aim to wrap up this week could make or break an export industry boom built up over the last 20 years that is now worth $60 billion. Trade ministers from the 12 countries negotiating the Trans-Pacific Partnership begin meeting in Atlanta on Wednesday and are on the cusp of sealing the biggest trade deal in a generation, cutting trade barriers and setting common standards for 40 percent of the world economy. The deal, a legacy-defining achievement for U.S. President Barack Obama, hinges on overcoming deadlocks over trade in dairy, drugs and autos -- sticking points that represent the sweet spot the deal must find between opening new markets, shielding existing industries and drafting new rules for issues ranging from intellectual property to labor rights. The deal will have to protect a Mexican auto industry that emerged as the North American Free Trade Agreement locked Mexico and Canada into the supply chains for U.S. carmakers - and increasingly their Japanese competitors, who manufacture there to avoid U.S. import duties of 2.5 percent on Japan-made cars. That tax will be phased out under the TPP, sparking fears in Canada and Mexico that low local content thresholds for autos will hand too much advantage to rival supply chains in Asia. Allowing cars with as little as 30 percent content from TPP nations to escape import duties, as proposed by Japan, would allow Japanese automakers to source parts in Asia and bypass Mexico, industry sources said. "(That) would be opening our market in a way that means businesses here could not compete with Asian firms," said Manuel Montoya, director general of the Automotive Cluster of Nuevo Leon, an industry group which lists among its members companies ranging from Daimler to smaller manufacturers of batteries, lubricants and moulded plastic. Mexico is vulnerable on high-volume, low-cost parts also produced in low-wage countries like Thailand, a key supplier for Japanese auto makers, or China, which currently has 13 percent of the U.S. imported auto parts market compared with Mexico's 34 percent, but is growing. Oscar Albin, executive president of Mexico's National Autoparts Industry (INA), said a 30 percent threshold would reduce exports to the United States, which enjoy a NAFTA standard roughly twice that high, by more than a third. The hardest-hit sectors would be makers of automotive cable harnesses, part of the electrical system, which account for $7 billion in exports, and car seat covers, he said. A person briefed on the talks said he expected the final threshold to be higher than 30 percent, though it would give carmakers more flexibility to source outside the TPP bloc. "I don't think they come away empty handed this time," he said. A final accord, which has been six years in the making, will need the blessing of the politically-powerful auto industries in the United States and Japan, the two biggest economies in the bloc, and Canada, home to auto parts makers Martinrea International and Linamar Corp. Canadian Prime Minister Stephen Harper, who faces a knife-edge election next month, said on Tuesday he would only sign a deal that secured auto markets for Canada's industry. "Cautiously Optimistic" Autos are one of a clutch of thorny issues ministers must resolve to seal the deal. A senior Mexican official said the prospects of closing were "very high," although for others close to the talks it was more of a 50-50 proposition. One senior Japanese government official said time was also running out with the 2016 U.S. presidential race looming, which will make it difficult for a Republican-led Congress to approve any trade deal, let alone one pushed by Obama, a Democrat. "If member nations cannot reach an agreement this time, it could take years," he said. U.S. Trade Representative Michael Froman said the United States would not accept a weak TPP deal, regardless of time pressures. "I think it's possible it's not going to work, but I'm on the 'cautiously optimistic' end of the spectrum," said Matthew Goodman, a former Obama administration official now at Washington's Center for Security and International Studies. There are signs of movement on the other major sticking points of dairy trade and rules preventing speedy knock-offs of next-generation biologic drugs, made from living cells. A source close to the talks said Ottawa rejected a push by Washington for access equivalent to 10 percent of the domestic dairy market. On drugs, TPP countries are divided over a 12-year monopoly sought by the United States and the five years in place in countries like Australia, for whom even a compromise on eight years would add millions to the cost of public health schemes.