By Foo Yun Chee BRUSSELS (Reuters) – EU antitrust regulators are asking Facebooks rivals and telecoms operators whether the world No. 1 online social networks proposed $19 billion bid for mobile messaging startup WhatsApp will lead to price hikes and curb innovation. The move came after Facebook sought EU approval for the deal, the largest in its 10-year history, which will give it a strong foothold in the fast-growing mobile messaging market and pit it against telecoms companies. The European Commission said on Monday it will decide by Oct. 3 whether to clear the deal unconditionally, demand concessions or extend the preliminary review into a wider probe. In a questionnaire sent to third parties and seen by Reuters, the EU regulator asked if the deal would have a negative, neutral or positive impact on users and customers in mobile messaging and social networks.