If a government shutdown happens, it'll be because Republicans are demanding policy restrictions in addition to spending cuts before agreeing to fund the government through September. These policy restrictions would target abortion providers and seek to limit the reach of the Environmental Protection Agency.

Which of the so-called riders are at stake and how do they work?

There are several riders addressing abortion and environmental regulation. It's not clear yet which of them specifically are at issue. Neither side is saying publicly which they are. But here's a primer on what they contain:

Abortion

The abortion rider that's received the most attention would prohibit the government from giving any money to Planned Parenthood.

That passed as an amendment on the House floor. However, written into the base bill is a provision that would eliminate Title X — a program that provides funding for family planning clinics across the country — altogether.

But there's one in there, too, which would prohibit the city of Washington, D.C., from using its own, non-federal funds to pay for abortions, beyond the accepted limits for the use of federal funds — rape, incest, or life of the mother.

It also blocks funding for the U.S. Ambassador's Fund for Cultural Preservation, the UN Population Fund, and any foreign NGOs that use non-U.S. funds to provide abortions.

The Environment

Before the House passed its spending bill, it tacked on several anti-environmental amendments to limit EPA authority. In particular, Republicans want to prevent the EPA from complying with a Supreme Court ruling requiring it to regulate green house gas pollution.

One section of the base bill would prevent the EPA from proposing, implementing or enforcing rules to mitigate emissions of climate pollution.

On top of that additional specific amendments would block the EPA from limiting, or tightening limits on, toxic cement plant emissions and particulate emissions. Rep. Don Young (R-AK) secured an amendment that would exempt oil drilling activities in Alaska from EPA regulations.

Other riders would prevent the EPA from executing a plan to clean up the Chesapeake Bay, strip it of its power to prevent water pollution that endangers animals, and block them from setting regulations regarding the containment and handling of coal ash.

There are other environmental riders in the bill that seek to limit other agencies. Here's a full list.

There are scores of other policy restrictions in the bill, too. But it the are the ones in the way of a deal to prevent a government shutdown.

Republished with permission from TalkingPointsMemo.com. Authored by Brian Beutler. Photo via AP. TPM provides breaking news, investigative reporting and smart analysis of politics.