European antitrust regulators will deliver their decision on Facebook’s proposed $19 billion acquisition of WhatsApp on 3 October this year.

The European Commission was officially notified of the deal on 29 August and is reported to have sent out a second round of questionnaires to rival companies to gain their opinion on whether the deal would lead to price rises and restrict innovation.

The move marks the start of the formal review of the deal, after which the regulator could decide to launch a more detailed investigation or wave the deal through.

The Wall Street Journal said the latest questionnaires are more detailed than the first batch sent in July, suggesting officials want to fully understand the distinction between a social network and messaging app to make an informed decision about Facebook and WhatsApp.

The questionnaires are likely to have been sent to mobile operators, social networks and ISPs identified as operating in at least one of the markets concerned. The companies are believed to have until 8 September to provide responses.

An EC spokesman would not comment on the questionnaires when approached by Mobile World Live.

It was reported in July that the Commission had sent out detailed questionnaires with the aim of gauging how the deal could potentially impact competition in the market.

It was Facebook itself that asked the EC in May to conduct a review covering all 28 countries within the EU to avoid the possibility of separate reviews in multiple markets.

Facebook said at the end of July that it may extend the deadline for closing the WhatsApp deal to 19 August 2015 if the applicable closing conditions, other than certain regulatory approvals, have been satisfied.

It added that it expects this to be the case and that the deal should close during the second half of 2014.

The US Federal Trade Commission (FTC) cleared the deal in April, but notified Facebook and WhatsApp about their obligations to protect consumer privacy, including the fact that post-merger WhatsApp must continue to honour prior promises made to consumers.

Analyst firm Ovum said it doesn’t expect the deal to be overly troubled by the EC but said it could result in further guidelines around personal data protection for WhatsApp users.

“WhatsApp needs to ensure that personal data is protected at all times, as any misuse or leakage of data could cause WhatsApp to lose its market leader status to strong competitors such as Line and WeChat that are not too far behind,” wrote senior analyst Neha Dharia in a research note.

Ovum has estimated that services like WhatsApp cannibalised SMS revenue by more than $32.5 billion globally in 2013. It also noted the expected release of the WhatsApp voice calling service could see regulatory intervention in markets where mobile VoIP is not yet popular.