All of them were fired by the police chief. And all of them were rehired after an arbitrator overturned their dismissals -- in a process laid out in the contract between the city and the powerful police union. 

In more than four out of 10 of the cases in which arbitrators ruled on officer terminations over the last decade, those firings were overturned, according to data provided by the San Antonio police department.

"We've seen too many cases where the arbitrator has overturned the chief's decision when it's as clear as day that that officer accused of misconduct should no longer be on the force," Ron Nirenberg, the city's mayor, told CNN. "It's egregious."

San Antonio is hardly an exception: Around the country, police unions have played a decisive role in shaping department policies and shielding bad cops from accountability, experts say. 

Now, as protests over the police killing of George Floyd have refocused national attention on police misconduct, unions representing officers are facing a wave of new scrutiny and an unprecedented political backlash.

More than 85% of police contracts in major cities around the country include language limiting oversight or discipline of officers, according to an analysis by Campaign Zero, a criminal justice reform advocacy group.

Often negotiated behind closed doors, contracts in some cases are approved by local politicians whose campaigns have been bankrolled by the same unions they're dealing with.

And police unions have only grown in financial power in recent years: The total assets of 56 large city police unions jumped by almost a third between 2011 and 2017, according to a CNN analysis of IRS tax filing data. 

In the wake of Floyd's death, however, the tide has started to turn, with some cities moving to reform their collective bargaining procedures and labor activists edging away from their police colleagues.

Stephen Rushin, a Loyola University Chicago law professor who has studied police unions and contracts, said a national rethinking of the role of police unions could have a significant impact in holding more cops accountable. 

"This moment feels different," he said. "This could be a really important inflection point."

How union contracts block accountability

In cities around the country, police officers are some of the most difficult government employees to fire thanks to favorable contract provisions negotiated by local unions. 

Contracts block accountability in various ways: Some ban civilian oversight or require disciplinary records to be destroyed. Others put limits on internal investigations, give officers advance notice for interrogations or require the city to pay if officers are held liable for misconduct in court. 

Rushin, who analyzed more than 650 police union contracts around the country, found in a 2019 paper that more than two thirds of the contracts forced police departments to go through an appeals process when they wanted to fire or discipline officers, placing