A $2.2 trillion business tax break Congress is eyeing could be the next measure to divide Republicans and business.

The provision, known as "full expensing," would allow companies to deduct the cost of all new investments from their taxable income in the year they are made.

It's an idea generally backed by conservatives. Last week, Texas Sen. Ted Cruz staked out the position that it should be part of the tax package. House Speaker Paul Ryan and Ways and Means Chairman Kevin Brady also have long advocated it, on the idea that it would spur business investment, the key to economic growth.

Yet, some big businesses are ambivalent about the idea.

Some fear that including a measure that big — the Tax Foundation estimated that it would decrease revenue by $2.2 trillion in a decade — would force taxwriters to scale back their ambitions for lowering corporate tax rates. Others, especially in real estate, worry that to get full expensing, they would have to give up other tax breaks they currently enjoy, especially the ability to deduct payments on debt.

And on the Right, the network of groups affiliated with the Koch brothers, and Koch Industries itself, has activated to try to block full expensing in favor of deeper cuts to business tax rates. The network played a key role in spiking the Ryan-led idea of a border-adjusted corporate tax, demonstrating its ability to shape legislative affairs.

On Thursday, one of those groups, Freedom Partners, released an analysis arguing that full expensing is an "untested" measure for generating economic growth compared to lowering tax rates.

"Any provision that stands in the way of lower rates would undermine our competitiveness and jeopardize the jobs, economic growth and opportunity we'd otherwise achieve," said the group's vice president of policy, Nathan Nascimento.

Similarly, in August, Koch Industries commissioned a report from the law firm Clark Hill concluding that rate cuts were a more reliable pathway to growth than expensing. A spokesman for Koch Industries said that the push for full expensing is an "impediment to lower rates."

Most right-of-center groups are on the other side of the issue. In June, a range of conservative groups, including Freedomworks, Heritage Action, and Americans for Tax Reform, signed onto a letter calling on Congress to implement full expensing.

Key to the pro-expensing argument is that it and low rates are even better if included together.

"While many of you, and certainly many in the business community, may see some of these policies as competing for space in a tax plan, we see those pieces as complementary and essential, not in conflict," Tax Foundation President Scott Hodge testified before the Senate Tuesday.

In particular, full expensing costs less to the Treasury if the tax rate is lower, noted Brandon Arnold, executive vice president of the National Taxpayers Union.

"These are the most important provisions," Arnold said of lower rates and expensing. "We need to fight to keep them both in and then make concessions elsewhere."

One problem is that some of the biggest companies that would benefit from being allowed to immediately write off new investments have made the political calculation to fight now for lower rates above all else.

"The most effective mechanism for driving investment ... is getting the rate down," said AT&T CEO Randall Stephenson, speaking Wednesday at an event hosted by the Business Roundtable. "That should be priority one."

Stephenson's company is regularly among the companies with the biggest capital expenditures in the country and plans to invest about $22 billion this year, even without expensing.

AT&T and several of the other companies with the biggest capital expenditures, such as Verizon, FedEx, UPS, Boeing, and Ford, are members of the RATE Coalition, a group formed to advocate for lowering the corporate tax rate. "We exist to focus attention on the corporate rate, which is the highest in the world — and that's a real problem," said Jim Pinkerton, co-chairman of the group. "If that problem gets fixed, and we're confident that it will, then we believe that all other tax issues can be resolved, too."

Several members of the group individually explained that their priority is first getting rates down.

"While we believe that lowering the tax rate and full expensing are both important, between the two, we believe lowering the rate is of primary importance," a representative for UPS said. "Our investment decisions are based on the long term, and while expensing no doubt provides a significant cash flow benefit, it does not provide real competitive tax reform."

One advantage businesses with big capital expenditures enjoy at the moment is that there have yet to be serious suggestions of going in the opposite direction and actually requiring companies to write off investments over a longer timeframe.

Under the current tax code, most businesses depreciate capital purchases according to a complicated schedule. For example, if a business buys new land, it is allowed to deduct a small part of the cost of the land each year for decades. A new machine might depreciate over a few years, as it produces profits and earns back its cost for the company.

In a draft tax reform bill released in 2014, then-Ways and Means Chairman David Camp proposed lengthening those schedules to pay for lower corporate tax rates.

It was an idea that helped the legislation balance, on paper. But, in the models used by tax economists, it crimped economic growth by penalizing new investment.

Now, advocates of full expensing think that Congress has ditched the idea of using longer depreciation schedules to pay for lower rates.

The joint statement released in late July by the "Big Six" of congressional Republicans and Trump administration officials working on tax reform called for "unprecedented capital expensing," even if it stopped short of endorsing full expensing.

Taxwriters on committees in the House and Senate are not likely to depart from that goal once they begin writing legislation. There's "not much apparent desire on either committee to go back to where Camp was," said Jim Gould, an adviser to the CRANE Coalition.

The coalition includes industry groups and companies, such as Comcast and Phillips 66, that want to retain existing measures within the tax code that have allowed companies to write off investments faster. For example, since the early 2000s, companies have been granted "bonus depreciation," which now allows them to immediately write off half the value of new investments.

In other words, businesses could be in a position to get a rate cut, while holding onto preferential depreciation rules.