As Washington weighs new cybersecurity steps amid a public backlash over mass surveillance, U.S. tech companies warned President Barack Obama not to weaken increasingly sophisticated encryption systems designed to protect consumers' privacy.In a strongly worded letter to Obama on Monday, two industry associations for major software and hardware companies said, "We are opposed to any policy actions or measures that would undermine encryption as an available and effective tool."The Information Technology Industry Council and the Software and Information Industry Association, representing tech giants, including Apple Inc, Google Inc, Facebook Inc, IBM and Microsoft Corp, fired the latest salvo in what is shaping up to be a long fight over government access into smart phones and other digital devices.