Senate Republicans passed their tax bill early Saturday, so the next step will be a conference committee with the House to iron out differences with a bill that passed  there on Nov. 16.

Some of those differences are dollar amounts, with each chamber setting brackets and deductions differently. But there are also substantive differences that could face push-back from House members, particularly conservatives, that have to be resolved before a bill could reach President Trump’s desk.

According to an internal poll of the conservative House Republican Study Committee obtained by USA TODAY, members were most concerned that the Senate bill sunsets individual tax cuts after 2025, delays the reduction in corporate rates until 2019, and continues to charge a tax on high-dollar estates.

The House could just pass the Senate bill and send it to Trump next week, but 97% of study committee members oppose that, and they’re not alone.

“We’re gonna go to conference unless the Senate makes unbelievable changes to their bill in the next few days,” Rep.  Mark Meadows, R-N.C., who chairs the hard-line House Freedom Caucus, told reporters Thursday.

Meadows said there did not seem to be any irreconcilable differences, however.

“I’m very optimistic,” Meadows said. “On a scale of one to 10, with 10 being the highest that tax reform gets done, I’m at a nine.”

He said he expected a bill on Trump’s desk by the end of the year.

But before that happens, here are some of the rough edges that must be smoothed out.

Corporate rate delay

One of the most significant sections of the bill is the massive tax cut for corporations. Both bills would take the top corporate tax rate from 35% to 20%. However, the Senate cut would happen in 2019, while the House bill would have the 20% rate kick in next year.

When the Senate unveiled its bill last month, Wall Street reacted to news of the delay with a 100-point drop in the Dow Jones Industrial Average.

Conservatives see no reason to delay what they believe will be an economic boom from cutting the corporate tax, and some worry about the impact on next year’s midterm elections.

“It would mean that the economy wouldn’t improve like it needs to so we would lose the majority in the House and Senate, but the Democrats would take power just in time to take credit for the economy improving because of what the Senate did,” Rep. Louie Gohmert, a hardline conservative from Texas, told reporters Thursday.

Elimination of the estate tax

Currently estates up to $5.5 million are exempt from taxes, but both the House and Senate bills would raise that number to $10 million, at least to start. However, the House bill would increase the exemption above $10 million each year after next year, and eventually eliminate the estate tax after six years.

The Senate bill would leave the tax in place for estates over $10 million.

While the estate tax disproportionately affects a small number of high-income earners, it has become a priority of Trump’s. At a tax event in Missouri this week, Trump said it would be helpful for “loving families” to help their children.

“We want to make it easier for loving families to pass on their life’s work to their children. Be nice. Be very nice, right?” Trump asked

House conservatives are expected to demand elimination of what they call “the death tax” in its entirety.

Repeal of the individual mandate

The Senate includes a repeal of the Obamacare provision that calls for an IRS fine on people who do not purchase insurance. The House bill did not, but not necessarily because of pushback from members. Trump started pressing for it to be included in a tax bill after the House had already crafted its bill.

Senate Republicans then included the provision in their tax bill and some moderates, like Sens. Susan Collins of Maine and Lisa Murkowski of Alaska, expressed concerns.

The Congressional Budget Office estimated that within 10 years, 13 million fewer people would have insurance and those who buy it from government-managed exchanges would see rates increase by 10% a year because the pool of patients would be sicker as healthier people opted not to buy coverage.

Collins and Murkowski were calmed by promises from Senate leadership and the president that Congress will advance a pair of separate bills intended to keep premiums down.

Because the House passed a repeal and replacement of Obamacare earlier this year that included eliminating of the individual mandate, such a provision isn’t expected to get significant enough pushback to be removed. However, expect some moderate House Republicans to follow the example of Collins and Murkowski in calling for separate bills to stabilize the marketplace.

And those bills will face pushback in the House where conservatives believe any subsidies are a bailout to insurance companies.

Immigration

Like the insurance promises that Collins and Murkowski got, Sen. Jeff Flake of Arizona voted for the tax bill in part because he was promised he would be part of a Republican effort to prevent deportation of undocumented immigrants who were brought to the United States as children.

Flake did not say he was promised a bill to protect so-called “DREAMers” would be passed before the tax bill. But it is not clear the House would make passage of such a bill a priority at all.

Sunset on individual rates

Where the House bill made most of its changes to brackets, credits, deductions and rates for individuals and families permanent, the Senate bill imposes them only for five years, after which the current tax code would kick back in.

That change, like the delay in the corporate reduction, was aimed at keeping the cost of the overall tax package from exceeding a $1.5 trillion limit set by the budget resolution adopted in October. It is something of a gimmick, since sponsors expect the tax cuts would be extended before they expire.

But the so-called “sunset” provision was the No. 1 criticism of the Senate bill by the House Republican Study Committee members. But if the conference committee changes it, that could push the total cost of the bill over the $1.5 trillion limit.