WikiLeaks is fighting back in an escalating war with both Google and the US government, threatening legal action the day after demanding answers for the tech giant’s wholesale handover of its staffers’ Gmail contents to US law enforcement.

The targets of the investigation were not notified until two and a half years after secret search warrants were issued and served by the FBI, legal representatives for WikiLeaks said in a press conference on Monday.

“We’re looking at legal action not only with Google but to those who actually turned in the order,” said Baltasar Garzón, the head of Julian Assange’s legal defence team. Calling the order illegal and arbitrary, Garzón said insisted “any information that would be used from the taking of documents [this way] will be considered as biased, illegal and will cancel the whole proceedings.”

“I’m not sure what craziness – what desperation – went into the US to make them behave this way, but this is … a clear violation of rights,” Garzón said.

“Our policy is to tell people about government requests for their data, except in limited cases, like when we are gagged by a court order, which sadly happens quite frequently,” a Google spokesperson said in a statement to the Guardian. “We’ve challenged many orders related to WikiLeaks which has led to disclosures to people who are affected. We’ve also pushed to unseal all the documents related to the investigation.”

Michael Ratner, a member of the Assange legal team in the US and president emeritus of the Center for Constitutional Rights, said that WikiLeaks had sent a letter to Google’s executive chairman, Eric Schmidt, asking why the company waited so long before notifying the targets of the warrants.

On Monday, Ratner went further, saying that WikiLeaks would decide on what legal action to take depending on Google’s response to the letter, which he said was expected within a week.

The notification of the court order was sent by email from Google to WikiLeaks on 23 December 2014 – just before Christmas, a typically quiet time for the news cycle – and was published on WikiLeaks’ site. Google said the legal process was initially subject to a nondisclosure or “gag” order that prohibited Google from disclosing the existence of the legal process.

Ratner told the Guardian that there were several questions as to what that legal process entailed. “Did Google go to court at all?” Ratner said. “Would they have notified us that that ‘we went to court and we lost?’ I don’t know.”

“If they didn’t go to court, that would not be a great move by Google, because you would expect them to litigate on behalf of their subscribers,” he said.

“Perhaps after the Snowden revelation, Google got nervous and decided to go to court,” Ratner added. “My big thing is: did they go to court initially? If they didn’t, I would consider that a real failure.”

The Google court order targeted three WikiLeaks employees: journalist Sarah Harrison, spokesperson and journalist Kristinn Hrafnsson and editor Joseph Farrell.

The wide-ranging scope of the order meant that all email content, including deleted emails, drafts, place and time of login, plus contact lists and all emails sent and received by the three targets – for the entire history of their email account up to the date of the order – had to be handed over to the FBI.

In a press conference, Harrison said that nobody at WikiLeaks would use Gmail accounts for sensitive information, but that the US government was “blanket going after a journalist’s personal account, fishing for something that could help them”.

Legal representatives from WikiLeaks on Monday repeatedly pointed – as an example of best practices for technology companies responding to US government requests – to Twitter, which in 2011 notified the target of a similar demand from law enforcement so that the warrant could be fought in court.

While the attempted challenge ultimately failed, Twitter was able to immediately notify its subscribers that their data had been handed over, and provide them with a copy of everything that had been provided to law enforcement.

In its statement to the Guardian, Google’s spokesperson said: “We continue to argue for surveillance reform which would enable us to be more transparent.”