The Environmental Protection Agency is demanding that Texas tighten its pollution laws. The EPA says the state, which is the top carbon-dioxide-emitter in the country, has air-quality regulations that break federal law, and it's studying whether oil refineries emit dangerous levels of toxins. Texas says its simpler regulatory system, which regulates facilities rather than individual smokestacks, is more efficient, but environmentalists say the rules are too lax. Air quality fights are intense in Texas; Houston and Dallas have violated federal air-quality standards for years, and city officials are cheering the EPA's move. But businesses aren't. The EPA has become far more aggressive under the Obama administration, and has said it will regulate carbon-dioxide emissions, set tougher limits on mercury emissions, and has held up dozens of permit applications for Central Appalachian coal mining projects. Business groups say the agency's mandates are too expensive and could drive jobs overseas.