WASHINGTON, July 29 (Reuters) - The White House has told U.S. automakers it wants them to back a voluntary target of at least 40% of new vehicles sales being electric by 2030 as it works to reduce greenhouse gas pollution, sources briefed on the matter said. The discussions with U.S. automakers on electric vehicle (EV) targets come as the Biden administration is set as early as next week to roll out its proposed revisions to vehicle emissions standards through 2026. Sources said a voluntary target could be as high as 50% but emphasized that no agreement with the automakers has been reached and many details remain under discussion, including whether that target will include only fully electric vehicles or partially electric vehicles that could also have a gasoline engine. United Auto Workers spokesman (UAW) Brian Rothenberg said a published report was inaccurate "that we have agreed to 40% EVs by 2030. The UAW is still in discussions and has not reached agreement at this point." The UAW has opposed EV mandates, warning it could put some jobs at risk. Earlier this month, Stellantis (STLA.MI) - the parent company of Fiat Chrysler - said it was targeting over 40% of U.S. vehicles be low emission by 2030. Stellantis declined to comment on Thursday. General Motors Co (GM.N) declined to comment on the talks. It has said it aspires to end sales of new U.S. gasoline-powered light duty vehicles by 2035. The White House declined to comment on the discussions. Ford Motor Co (F.N) did not immediately respond to a request for comment. The Biden administration has resisted calls from many Democrats to set a binding target for EV adoption or to follow California in setting 2035 as a date to phase out the sale of new gasoline-powered light duty vehicles. The National Highway Traffic Safety Administration (NHTSA) and Environmental Protection Agency (EPA) are reviewing then President Donald Trump"s March 2020 rollback of fuel economy standards to require 1.5% annual increases in efficiency through 2026, well below the 5% yearly boosts set in 2012 by President Barack Obama"s administration. The proposed rules, which will cover 2023-2026, are expected to be similar in overall vehicle emissions reductions to California"s 2019 deal with some automakers that aims to improve fuel economy 3.7% annually, sources told Reuters. The 2026 requirements are expected to exceed the Obama-era 5% annual improvements. In March, a group of 71 U.S. House Democrats urged Biden to set tough emissions rules to ensure that 60% of new passenger cars and trucks sold are zero-emission by 2030. The United States pledged at a global climate summit earlier this year to reduce emissions 50% to 52% by 2030, compared with 2005 levels. In April, a dozen governors from states including California, New York and Massachusetts, urged Biden to endorse banning new passenger gasoline-powered vehicle sales by 2035.