President Donald Trump today took to Twitter to question the future of his government's premier domestic surveillance tool ahead of a key vote, only to make a spectacular U-turn an hour later. The US leader voiced opposition to rules that allow agencies to monitor foreign terror or spy suspects, as long as they gather a court order. The so-called 702 authority was put in place after the 9\/11 attacks. Although controversial, officials from Democratic and Republican administrations have argued the eavesdropping tool is vital to counterterrorism and counterespionage efforts and has saved lives - an argument echoed by Trump's own White House. But, apparently quoting a Fox News headline, Trump tweeted that the "House votes on controversial FISA ACT today" and expressed concern that it was used under Barack Obama's presidency to spy on him, a charge strongly denied by the former administration. "This is the act that may have been used, with the help of the discredited and phony Dossier, to so badly surveil and abuse the Trump Campaign by the previous administration and others?" Trump wrote. Americans cannot be the subject of 702 surveillance, but can be picked up in the surveillance of foreign targets. Until that tweet, the Trump administration had strongly pressed Congress to extend the authority, before it lapses on January 19. Just hours before Trump's tweet, the White House had urged lawmakers to oppose new rules that advocates say could gut the programme. "The Administration urges the House to reject this amendment and preserve the useful role FISA's Section 702 authority plays in protecting American lives," the White House said in a statement. Earlier in the week, Trump had himself signed an order to review the way that Americans caught up by surveillance can be identified - or "unmasked" in the jargon. As Trump's morning tweet sent shockwaves through Washington, the president once again took to Twitter, this time to voice support for the 702 authority. "With that being said, I have personally directed the fix to the unmasking process since taking office and today's vote is about foreign surveillance of foreign bad guys on foreign land. We need it! Get smart!" he tweeted.