The EPA and California Air Resources Board have moved slowly in the past year, failing to reach a consensus on key issues between the federal department's proposals to roll back emissions-based fuel economy standards and the state's decades-old ability to set their own.

Tensions boiled over this week when EPA Administrator Andrew Wheeler sent a note to Congress on Thursday accusing the state regulatory agency of failing to negotiate in good faith and misrepresenting negotiations between the federal agency.

"I believe it is important to understand that when Mrs. Nichols states that she offered a counterproposal to the proposed rule as if she operated a good faith actor in this rulemaking, that is what is false," Wheeler wrote in the letter.

Wheeler also said that the EPA reached out to California regulators several times during negotiations with no response, and that the state delayed its counterproposal for weeks. Wheeler also said that Nichols' written testimony amounted to "conspiracy theories" about the EPA and that her conduct was "beneath the responsibilities of the substantial position she holds." According to Reuters, Nichols denied the claims.

The long-running feud between the two agencies effectively may put the proposed EPA rollbacks on a collision course with courts, where the standards may ultimately be decided. EPA officials signaled that the final proposal may be submitted to the White House for final review within weeks, likely including a provision to strip California of its waiver to set clean-air standards for its own state and roughly a dozen others that have adopted the similar rules.

California Air Resources Board chair Mary Nichols (via Twitter)

California Air Resources Board chair Mary Nichols (via Twitter)

If the two sides don't reach an agreement within the next few weeks, it's likely that the new regulations would face stiff challenges in courts, and place in limbo the country's future emissions and fuel-economy targets that would give automakers no clear target for domestic vehicle development for years—a course they've vehemently opposed.

This month, 17 of the biggest automakers in the world sent a note to the White House and urged the administration to compromise with the state between its proposal and the state's stricter rule standards.

After Thursday it's unclear if the administration is willing to make a deal or ultimately push its proposal through—or, more likely, to the courts.

"I am really not interested in a pissing contest between California and this administration," Michigan Rep. Debbie Dingell said Thursday, according to Reuters.