The federal government will shut down at midnight on Friday, barring an unexpected, last-minute bipartisan deal. That puts medical marijuana patients and providers at risk of being arrested, prosecuted and sent to prison by Jeff Sessions’s Justice Department.

Here’s why:

Under a shutdown scenario, an existing budget provision that prevents the Drug Enforcement Administration (DEA) and other agencies from spending money to interfere with state medical cannabis laws would expire. But federal drug enforcement and prosecution actions, which are exempted from furloughs, would continue.

Why Might The Government Shut Down?

A bill to extend federal funding levels and policy riders like the marijuana one through February 16 was approved by the House on Thursday. But a heated dispute over immigration issues has jeopardized its passage in the Senate, where a significant number of Democrats are refusing to support any bill that does not provide protections to people who were brought to the U.S. as children.

Earlier this month, Attorney General Sessions rescinded Obama-era guidance that has generally allowed states to implement their own cannabis laws without federal intervention. That has left recreational marijuana businesses and consumers without a key protection they’ve relied on since 2013, but the ongoing existence of the medical cannabis spending rider has continued to keep patients and providers safeguarded from federal attacks.

Until now.

An unintended consequence of Senate Democrats’ move to block the funding extension bill and shut down the government over immigration issues is that medical marijuana patients and industry operators would be at much greater risk, as soon as this weekend.

Why Would Drug Enforcement Continue Under A Shutdown?

“All agents in DEA field organizations are excepted from furlough because they support active counternarcotics investigations. This encompasses 21 domestic divisions, 7 regional foreign divisions, critical tactical support groups including the El Paso Intelligence Center and the Special Operations Division, forensic sciences, and technical surveillance support,” a Justice Department shutdown contingency plan says. “DEA investigations need to continue uninterrupted so that cases are not compromised and the health and safety of the American public is not placed at risk.”

The same goes for federal prosecutors.

“As Presidential Appointees, U.S. Attorneys are not subject to furlough,” the shutdown document reads. “Excepted employees are needed to address ongoing criminal matters and civil matters of urgency throughout the Nation. Criminal litigation will continue without interruption as an excepted activity to maintain the safety of human life and the protection of property.”

Politics Of Marijuana And Immigration Collide

Democrats, especially those considering 2020 presidential bids, are facing enormous pressure from their progressive base not to go along with yet another bill in a series of short-term funding extensions that do not include protections for young immigrants known as “DREAMers.” Because Republicans hold only 51 seats in the chamber, and a handful of GOP members are also opposing the spending resolution, leaders need support from Democrats to reach the critical 60-vote threshold to advance legislation.

The medical cannabis budget rider was first enacted into law in late 2014, and has since been extended for each subsequent fiscal year. Last May, Sessions sent a letter to congressional leaders asking them not to continue the medical marijuana rider into Fiscal Year 2018.

“I believe it would be unwise for Congress to restrict the discretion of the Department to fund particular prosecutions, particularly in the midst of an historic drug epidemic and potentially long-term uptick in violent crime,” he wrote. “The Department must be in a position to use all laws available to combat the transnational drug organizations and dangerous drug traffickers who threaten American lives.”

Setting aside the important question of whether the medical cannabis rider will be included in full Fiscal Year 2018 spending legislation that congressional leaders continue to negotiate — and it is a big question, since House leaders blocked lawmakers from even voting on whether to include the policy in that chamber’s version of Justice Department spending legislation — the current budget brinksmanship on Capitol Hill means the medical marijuana protections could disappear as soon as Saturday morning.

A Shutdown Allows Old Federal Marijuana Prosecutions To Resume

If the provision lapses, it wouldn’t just allow new actions against people violating federal marijuana laws. It would also allow earlier medical cannabis prosecutions that were suspended under to the rider to resume.

A federal judge in a California case last August, for example, wrote that the prosecution of two marijuana growers would be “stayed until and unless a future appropriations bill permits the government to proceed. If such a bill is enacted, the government may notify the Court and move for the stay to be lifted.”

The failure to enact a new bill continuing the protections would have the same effect under a shutdown scenario, given that enforcement of federal drug laws would still continue.

Long-Term Status Of Marijuana Protections Unclear

The Senate Appropriations Committee voted in July to include the medical cannabis rider in its version of the 2018 Justice Department funding bill. But without the provision being approved on the House side, its long-term continuance will be determined behind closed doors by a bicameral conference committee that merges the two chambers’ proposal into a single bill to be sent to President Trump.

Advocates have also pushed to expand the protection to encompass all state marijuana laws, not just those focused on medical access. A measure to do that came just nine flipped votes of passage on the House floor in 2015, and the number of states with legalization has doubled since then. However, Republican congressional leaders have blocked subsequent cannabis measures from advancing to floor consideration, including as recently as this week.

In the meantime, medical cannabis patients and providers will wait to see if Jeff Sessions and his DEA agents will regain the ability to come after them for the first time since 2014 this weekend.

Portions of this post were first published by Forbes.