President Barack Obama's top labor arbiters have overturned a cumulative 4,500 years of legal precedent over the past eight years, according to a new study.

The National Labor Relations Board, an agency that oversees union elections and workplace disputes, has issued numerous new rules that changed longstanding agency practices, as well as issued decisions that overturned decades of precedent.

In all, the board has overturned 91 precedents, wiping out more than 4,000 years of case law—averaging more than 45 years per decision; the agency's new election rules overturned a combined 454 years of protocol, according to a study from three labor attorneys at the Coalition for a Democratic Workplace and Workplace Policy Institute.

Those decisions and new rules have radically changed workplace operations on everything from establishing micro-unions to dues withholdings to holding umbrella companies accountable for the behavior of franchisees or subcontractors to shortening the length of union campaigns and disclosure practices during elections.

The overturned precedents have been in lockstep with the labor agenda at the expense of standing law that had been previously untouched by appointees from both Democratic and Republican White Houses, according to the report.

"In each case where the Obama Board changed the law, the resulting new law became more favorable to labor interests than it did under previous Board rulings—frequently at the expense of promoting stable bargaining and economic growth and without regard for balancing the interests of business, labor and employees under the Act," the study says. "A high percentage of the precedent the Obama Board overturned were more than ten years old and had been previously adopted by Board members of both political parties."

The study, authored by Michael Lotito, the co-chair of the Workplace Policy Institute and a lawyer at Littler Mendelson P.C., and two other attorneys, found that the board "overturned established precedent in a largely partisan manner." The NLRB's five board members are appointed by the president with at least one or two appointments coming from the minority party depending on the current size of the board.

The study found that not one Republican joined the Democratic majority in any of the 91 cases that overturned major precedent, though Republicans board members joined the majority in other areas of case law.

The method by which the board overturned precedent also departed from general progression in labor law. Rather than building up case law and using those decisions to chip away at longstanding practices without running afoul the confines of the National Labor Relations Act, the Obama board was more likely to make radical changes in a single decision.

"The Board made no unanimous decisions to overturn, or substantially modify, important precedent during the time period in question," the study says. "The Board set a trend of overturning extensive precedent in a single case."

The method of overturning precedent has hurt the ability of the board to justify its decisions in federal appeals courts—where plaintiffs can appeal any board decision, though, as the report says, "a significant number of Board decisions are never appealed by adversely affected parties for a variety of reasons, including financial." In September, for example, Washington D.C. Circuit Court of Appeals Judge Janice Rogers Brown ordered the NLRB to pay a Michigan healthcare provider more than $17,000 for pursuing "bad faith litigation."

"The Board’s conduct before us manifests a stubborn refusal to recognize any law. The Board’s obstinacy forced Heartland to waste time and resources fighting for a freedom the Board knew our precedent would provide," the Appellate Court ruled. "Administrative hubris does not get the last word under our Constitution. And citizens can count on it."

Labor watchdogs said that the NLRB's reversal of longstanding precedent could leave it vulnerable when President-elect Donald Trump takes office and makes his own appointments. The lack of precedent to back up those decisions could leave them vulnerable before a Republican board or at the federal judiciary.

Heather Greenaway, spokeswoman at the Workforce Fairness Institute, said that the NLRB has acted as a "rogue agency" during President Obama's tenure.

"The Obama-era NLRB will be remembered as an anti-jobs agency that rewarded Big Labor cronies by rolling back years of long-standing precedent," she said in a statement. "We are hopeful that the incoming administration will reverse the damage caused by the Obama’s labor board by … promoting stable bargaining and economic growth, while also unwinding the damaging and job-killing rules leveled by pro-union bureaucrats."