It is unclear this afternoon whether controversial legislation to fund U.S. EPA and the Interior Department will return to the House floor as soon as tomorrow, or whether it will be scrapped in favor of votes on legislation related to the federal budget and deficit reduction.

The floor schedule was thrown into doubt this afternoon, when appropriators said Republican leadership might take up a constitutional amendment requiring a balanced federal budget, instead of the spending bill.

"What we've been told is [Interior/EPA bill] probably won't come up this weekend," Rep. Norm Dicks (Wash.), the top Democrat on the Appropriations Committee, said this afternoon.

Dicks also said he was uncertain whether the funding bill would return to the floor next week, before Congress leaves for its August recess.

Jennifer Hing, a spokeswoman for committee Republicans, said the schedule was "up in the air," and that appropriators hoped to know by tomorrow morning if the Interior and EPA bill would return to the floor.

But the bill (H.R. 2584) was never the top agenda item of the week, as Congress and the administration work to raise the federal debt limit ahead of Tuesday's deadline.

It does, however, provide a backdrop for a heated debate over whether federal regulators should act aggressively to reduce pollution or minimize their demands on business.

Before today, Democrats appeared to be scaling back their attempts to strike the bill's numerous policy riders limiting U.S. EPA and Interior Department regulations.

Earlier this week, Appropriations Interior and Environment Subcommittee ranking member Jim Moran (D-Va.) told reporters that Democrats planned to introduce 18 amendments to strike these provisions, but in the past two days, Moran and other key Democrats have said they are weighing their options.

Some of the highest-profile policy riders may not be contested. For example, the spending bill as written would place a one-year moratorium on EPA's Clean Air Act rules for both stationary sources and efforts to craft vehicle emissions limits for 2017 and beyond. Democrats had planned to offer amendments to jettison both provisions, but Moran said yesterday that might not still be the case.

"If we don't think we're going to get a good vote on it, we may not take it to a vote. We may just speak on it and not call for a vote," he said.

Moran said that in the likely event that the amendment fails, that might cast doubt on an agreement the White House reached earlier this week with automakers, unions and the state of California that would lead to a 54.5 mpg fuel economy standard for cars and light-duty trucks by model year 2025.

"We don't want to do anything to jeopardize that," he said. "If the vote looks like it might undermine our current position, we might want to think twice about taking it to a recorded vote."

Ryan Nickel, a spokesman for Dicks, said a final decision had not yet been made on greenhouse gas amendments or amendments to strike the bill's stay on EPA rules for particulate matter.

"Whether those amendments come up or not is still unclear," he said.

One amendment that Democrats do plan to offer would take a swipe at the bill's stay on EPA's proposed rule for mercury and other air toxics from electric utilities.

Rep. Lois Capps (D-Calif.), the amendment's sponsor, told reporters earlier today that she is appealing to colleagues on both sides of the aisle who are parents, because children and pregnant women are particularly vulnerable to mercury poisoning.

Capps said she had recently discovered through a test that her own mercury levels were high.

"You don't need to live next door to a dirty power plant to suffer the effects of dirty air pollution," she said. "If you block EPA mercury standards for power plants, it's going to translate into more deaths, more emergency room visits and more asthma attacks."

Capps was flanked by fellow Democratic Reps. Debbie Wasserman Schultz (Fla.), Jan Schakowsky (Ill.) and Doris Matsui (Calif.), who said they opposed the spending bill's language as mothers and grandmothers.

"If you think about our kids, we are their only defense," said Wasserman Schultz. "I just can't believe [Republicans] are jeopardizing the health of women and children."

Rep. Betty McCollum (D-Minn.) plans to offer an amendment stripping language from the bill exempting Texas from an interstate ozone rule.

Republicans, meanwhile, are preparing amendments to beef up the bill's prohibitions on spending for environmental regulations.

Rep. Austin Scott (R-Ga.) has offered an amendment that would defund all climate change-related programs in all the agencies covered by the bill.

Rep. Rick Berg (R-N.D.) would place a new stay on EPA authority to regulate haze.

Berg spokeswoman Alee Lockman said this afternoon that EPA's haze rules are an intrusion in Berg's state.

"North Dakota has established a regional haze management plan, under EPA guidelines, that would work best for our state's unique needs," she said. "However, the EPA has overruled North Dakota's plan and instead chosen to implement a costly, 'one-size-fits-none' policy based not on North Dakota's needs, but on the EPA's own national plan."

Reporters Jeremy P. Jacobs and Emily Yehle contributed.