China has threatened to retaliate if the European Union formally opens an investigation into alleged anti-competitive behaviour by Chinese mobile telecom equipment companies.The EU had warned earlier this week that it may investigate claims that Chinese telecom firms have been paid subsidies, allowing them to flood markets with cheap equipment, if bilateral negotiations fail. Beijing's commerce ministry spokesman Shen Danyang said yesterday that European mobile telecom equipment firms enjoy a much bigger market share in China than Chinese companies have in the EU, and any moves by Brussels will harm them both.China is the world's second-largest economy and the EU is its biggest trading partner.