WASHINGTON (Reuters) - Four of Washington’s largest business lobby groups urged Congress in a letter on Wednesday to settle their differences on government spending so they can move forward on overhauling the U.S. tax code in the next year.  The U.S. Chamber of Commerce, Business Roundtable, the National Association of Manufacturers and the National Federation of Independent Businesses penned a joint letter calling for lawmakers to adopt a budget for next year that would allow them to begin work on changing the tax code.      “In our view, given the historic opportunity before Congress, no other reforms under consideration rise to the importance of pro-growth, comprehensive tax reform,” the letter states. The budget process hit a delay this week after conservative Republicans in the House continued to demand billions of dollars in cuts to the spending outline.     Passing a budget is vital to begin the process of rewriting the tax code because it permits a procedural maneuver that will allow Republicans to pass a tax bill without the support of Democrats. President Donald Trump has made tax reform a key goal for this year. Additionally, Congress has become bogged down in trying to repeal Obamacare, a process that was delayed again this week and has been blamed for the inability to move on to tax reform. The joint letter urged Congress not to let other fights, alluding to health care, prevent tax reform from being completed this year.      