No California ballot would be complete without at least one measure about crime and punishment and 2020 will be no exception.

A referendum seeking to overturn California’s landmark ban on cash bail in criminal cases will once again test voters’ sentiments about the treatment of accused lawbreakers.

During previous decades, particularly in the 1980s and 1990s, voters endorsed a tough, lock-‘em-up attitude, culminating in passage of the state’s famous — or infamous — three-strikes-and-you’re-out law aimed at repeat offenders.

At some point — roughly a decade ago — voter attitudes about crime softened and criminal justice reform advocates began winning in the political arena.

When Jerry Brown returned to the governorship in 2011, he strived to undo some of the punishment laws he had signed three decades earlier by reducing penalties for crimes deemed to be nonviolent, diverting more offenders into probation rather than putting them behind bars and making it easier for felons to win parole.

Law enforcement officials objected, saying that fewer offenders behind bars would imperil the public, but in 2014, Brown won passage of a key ballot measure, Proposition 47, encompassing his reforms.

As his second governorship was ending last year, Brown also championed and signed legislation, Senate Bill 10, to eliminate cash bail — a long-sought goal of civil rights and criminal justice advocacy groups.

They argued that the bail system discriminates against the poor who are unable to either post bail themselves or afford the fees of private bail bond agents.

Under the legislation, those accused of minor, non-violent offenses would almost automatically be freed while awaiting trial and other defendants would be evaluated for their flight risk with judges having the final word on who would remain locked up.

SB 10 would, in effect, erase an entire industry, California’s 3,000-plus bail bond agencies, and, not surprisingly, they decided to fight back. Very quickly, a bail industry coalition raised money to qualify a referendum for the 2020 ballot to overturn the new law, whose implementation is now suspended until the voters have spoken.

Bail agents are clearly poised to spend millions of dollars to preserve their livelihoods and now the Service Employees International Union (SEIU) is committing itself to finance a pro-SB 10 campaign.

The SEIU has couched its support for SB 10 in terms of civil rights and protecting poor people from a rapacious industry. However, it also has a financial interest in the outcome because ending cash bail would mean adding thousands of new unionized workers to county probation departments for evaluating defendants.

So the stage is set for another political showdown on crime, with the particularly tricky procedure of a referendum. The question on the ballot will be whether voters want to keep SB 10 in force, so the bail agent coalition will be seeking a “no” vote while SEIU and other supporters will want voters to say “yes.”

Initially, it’s difficult to say which side has a better chance of prevailing. A statewide poll conducted by UC Berkeley’s Institute of Governmental Studies in September found that 39% of voters are inclined to vote “yes” to support the new law, while 32% are opposed and 29% are undecided.

There’s a partisan division, with Democrats in support and Republicans opposed, so that should give SB 10 supporters an edge. But voters now on the fence will have the final word and that’s where both sides will concentrate what is likely to be their emotion-laden appeals.