WASHINGTON (Reuters) - The Obama administration announced plans to expand wage reporting requirements for private businesses on Friday, bolstering its efforts to narrow the longstanding U.S. gender wage gap. The Equal Employment Opportunity Commission’s plan would require employers with 100 or more employees to provide the agency with detailed wage information, broken down by gender, race and ethnicity.    Unlike a similar Labor Department rule proposed earlier, it would apply to all large businesses and not just federal contractors. The plan, which is expected to take effect in September 2017, will be open to public comment but does not require congressional approval. It is part of a long-running effort by Obama and federal agencies to close the yawning gap between pay for men and women. The commission’s proposal would not require the disclosure  of specific salaries of individual employees, but it would seek aggregate data on pay ranges and hours worked. “The goal is to help businesses that are trying to do the right thing ... to get a clearer picture of how they can make sure their employees are being treated equally,” Obama said at a White House event. He spoke on the seventh anniversary of the Lilly Ledbetter Fair Pay Act. The measure, the first bill Obama signed into law, overturned a Supreme Court decision that severely restricted the time period for filing complaints of employment discrimination concerning compensation. Although fighting gender pay imbalances has been a focus for Obama, the pay gap has narrowed only slightly over the past two years. “We can’t deliver on the promise of equal pay unless we have the best, most comprehensive information about what people earn,” Labor Secretary Thomas Perez said in a statement on Friday. The median wage of a woman working full-time year-round in the United States is currently about $39,600, only 79 percent of a man’s median earnings of $50,400. Gender equality in the U.S. work force, and globally, is still decades away, according to an independent report released on Wednesday.  