A new OpenSecrets report has revealed some of the biggest donors to anti-marijuana legalization campaigns and politicians — and there's serious money involved. When marijuana reform laws are on the ballot in your state, you should know that people with a financial interest in keeping marijuana illegal are bankrolling those scare ads and anti-pot PSAs. Here are the five biggest groups OpenSecrets thinks have ulterior motives in mind for backing the War on Drugs.

1. Police unions

Police unions are major donors to anti-legalization efforts, probably because a major stand-down in the War on Drugs would disrupt huge sources of police funding. The Nation's Lee Fang identifies two major revenue streams that legal marijuana would disrupt: federal awards like Byrne grants ($2.4 billion in fiscal year 2014 alone) and marijuana-related property forfeitures (around $1 billion from 2002-2012).

OpenSecrets says that police unions helped bankroll Public Safety First, a group that opposed California's legalization initiative in 2010. Altogether, here's what their lobbying efforts have looked like since 2008 (numbers are annual minimums):

- National Fraternal Order of Police, $220,000

- National Association of Police Organizations, $160,000

- International Union of Police Associations, $80,000

- International Association of Chiefs of Police, $80,000

Altogether, that's a minimum of $540,000 a year in police union lobbying. While some of that money is meant to influence things like contracts and funding, all of these groups oppose drug law reform. NFOP executive director Jim Pasco thinks "The country is going to hell in a handbasket" while "these people are worried about getting high." Sheriff's associations nationwide, like Minnesota's, fight against even medical marijuana.

Cops themselves, for what it's worth, seem open to looser marijuana laws — a Law Officer magazine poll found 66% support some type of reform, while 37% supported legalization outright.

2. Private prison corporations

Prison sentences for drug users is big business and private companies that operate correctional facilities view drug law reform as a major threat to their bottom line.

According to OpenSecrets, since 2008 Corrections Corporation of America (CCA) has spent around $970,000 a year on lobbying, while competitor GEO Group has spent $240,000-660,000 a year on their legislative efforts. Both make more than a billion a year in taxpayer funding. CCA is an extremely close partner of the right-wing American Legislative Exchange Council, which the Nation writes "helped pioneer some of the toughest sentencing laws on the books today, like mandatory minimums for non-violent drug offenders, 'three strikes' laws, and 'truth in sentencing' laws." The company has also identified drug and immigration reform as threats to the industry's profit margins. For its part, GEO Group's low- and medium- security state prisons likely hold a large number of petty drug offenders.

3. Big Pharma

Pharmaceutical Research and Manufacturers of America is by far the biggest pharmaceutical lobbying group in the U.S. and OpenSecrets claims they spent close to $18 million on lobbying in 2013 alone (making it the ninth biggest lobbying client). Other groups spend millions more.

High Times argues that Big Pharma opposes marijuana legalization because they produce alternatives like Sativex, Marinol and Cesamet. But don't take it from them alone — Fang notes that Oxy-Contin manufacturer Purdue Pharma and other drug companies are huge sponsors of the Community Anti-Drug Coalition of America (CADCA) and the Partnership for Drug-Free Kids, which both take a "hard-line approach" on weed. CADCA energetically pushes for drug control grants and opposes even moderate steps like downgrading marijuana from its Schedule I status.

A medical director for pharmaceutical company Orexo sits on the board of Project SAM, which enthusiastically compares weed to tobacco — and which has an entire page promoting synthetic alternatives to medical marijuana. I mean, come on.

4. Prison guard unions

Prison guards' livelihoods depend on keeping prisoners behind bars, which might explain why OpenSecrets found their unions lobbying for legislation that puts and keeps people there. One Californian prison guard union spent a whopping $1 million fighting drug sentencing reform — probably because of a 25-fold increase in drug offenders in the state's jails from 1980-2001.

The American Federation of State, County and Municipal Employees (AFSCME), which represents 85,000 prison guards, spent over $13 million in 2012 and around $2.7 million in 2013. AFSCME actually isn't evil — it's one of the biggest public-sector unions, doesn't like private prisons and supports medical marijuana. But it nonetheless remains an obstacle to ending mass incarceration when prison closures threaten jobs.

For what it's worth, other prison guard groups actually support drug sentencing reform and scaling down the War on Drugs: Prison overcrowding seriously endangers their members.

5. Alcohol and beer companies

Typically, alcohol and beer companies only really care about things that directly affect them like blue laws, taxes and alcohol regulations, and their lobbying has generally focused on these issues. OpenSecrets notes that since 2009, the industry has spent at least $19.5 million a year on lobbying. California Beer and Beverage Distributors gave $10,000 to Public Safety First.

More broadly, legalization proponents have highlighted specific anti-pot candidates with ties to the beverage industry like Rep. Lamar Smith (R-Texas), while Alternet's Jodie Gummow documents a history of tension between the two industries — but mainly because pot proponents are fond of (accurately) pointing out weed is safer than drinking.

For now, Big Alcohol doesn't sense a big threat and is staying mostly out of the debate. But if legal marijuana becomes a big competitor to beer and liquor or studies provide further evidence that marijuana use causes people to drink less, this fight could get ugly fast.