House and Senate negotiators are working to complete a deal as early as this week that would revive dozens of expired tax breaks and could also seek to scale back a controversial part of Obamacare and expand some tax benefits for low income workers.

A bipartisan group of staffers from the House Ways and Means and Senate Finance committees worked throughout the Thanksgiving recess in hopes of hashing out an agreement to retroactively reinstate the expired tax breaks for businesses and individuals, extending many for a year while making some permanent, according to aides familiar with the negotiations. Early versions of the package circulated by lobbyists and staffers were estimated to cost as much as $700 billion over 10 years, but aides said the discussions are still preliminary and nothing is finalized.

“We’re working on it and we’ll get it done,” Senate Finance Committee Chairman Orrin Hatch (R-Utah) said on Monday.

The talks started before the holiday in hopes of finding a middle ground between a two-year extension of the nearly 50 breaks approved earlier this year by the Senate Finance Committee and calls by House Republicans to make about a dozen breaks permanent. The discussions are now focused on permanently extending the research and experimentation credit, small business provisions and breaks for charitable donations.

Several aides said the goal was originally to work out a deal in time to include the package in the upcoming highway funding bill that is due by Dec. 4 or the omnibus spending bill that must be completed by Dec. 11. But the legislation could also move as a separate stand-alone package to avoid complicating either must-pass bill.

Hatch said he hopes the legislation could be completed before the Dec. 11 omnibus deadline.

Extending the group of nearly 50 temporary tax breaks known as the extenders has become an annual headache for lawmakers. It is not uncommon for some or all of the breaks to expire, many of the provisions now being considered ran out at the end of 2014, and then be retroactively extended. While there is broad bipartisan support for extending the breaks, there is little consensus over whether they need to be offset with spending cuts and how long the extensions should last.

“Let’s do the art of the doable,” Hatch said.

Also under discussion is whether to expand the Earned Income Tax Credit for low-income workers to include more childless workers, something Democrats and some Republicans, including President Obama and House Speaker Paul D. Ryan (R-Wisc.), have said they would like to do. There is also some bipartisan support for expanding the existing child tax credit. But aides said Republicans are pushing for more rules to crack down on fraud, abuse and access to the credits for undocumented workers.

“It’s an important issue but I think we’ll find some resolution,” said Hatch, who added he is not sure the program will be expanded. “We know that EITC has fraud in it. On the other hand it is an important program that requires work.”

The Child Tax Credit sparked a heated fight earlier this year when the House passed an expansion of the program that would have required parents to provide Social Security numbers for any children they claim on their tax return. Democrats have said they could back some fraud and abuse controls, like barring those who mistakenly or fraudulently claim the credit from being able to receive it for two years, but they balked at this proposal.

Finding the middle ground could be difficult with immigration remaining a heated issue both in Congress and in the GOP presidential race.

Another potential sticking point is the debate over the Cadillac Tax, an excise tax on high-value employer-sponsored healthcare plans used to help pay for the president’s signature health care law. Republicans and many Democrats, including presidential candidates Hillary Clinton and Sen. Bernie Sanders (I-Vt.), dislike the tax but lawmakers still disagree over whether they want to delay its implementation or repeal it completely.

The tax also isn’t on the list of expired breaks and negotiators have been hesitant to expand the discussion beyond these policies, according to aides.

Republicans have long said they would like to permanently extend business tax credits for research, expensing and bonus depreciation as well as those for charitable donations. Those programs are some of the most costly items on the extenders list but some Democrats have been willing to support making them permanent in exchange for saving some clean energy credits and expanding programs for low-income workers.

Hatch said he expects the package will include a credit for wind energy production that is a priority for Democrats. But he said the program would be phased out as part of the deal.

The Committee for a Responsible Federal Budget, a watchdog group, estimates that an expanded extension of the research credit proposed by House Republicans would cost $180 billion over 10 years. The popular Section 179 business expensing provision could add another $70 billion over the same time period.

Even if negotiators do reach a deal, it is unclear if there will be enough support to add billions in tax expenditures to the already uneasy talks over the year-end spending package or the highway bill. Typically Republicans argue that Congress does not need to pay for extending existing tax breaks or creating new tax relief.

House Majority Leader Kevin McCarthy (R-Calif.) told reporters on Monday that he does not believe the breaks need to be offset

”I’m a firm believer that when it comes to taxes the more people can keep in their own pocket the more the economy moves faster,” McCarthy said.

Hatch said that he does not expect the bill will be offset.

But it is unclear if hard-line conservatives will accept that argument. Many have said that some of the tax breaks in question are aimed narrowly at special business interests and amount to corporate welfare. Those conservatives have not yet weighed in on the negotiations or said how they would respond if tax writers attempt to slip $700 billion of tax breaks into another legislative package, such as the already massive spending bill.