House and Senate lawmakers will begin considering a fiscal 2018 budget this week to start the Republican race to finish tax reform by the end of the year.

The budget resolution is one of the most critical measures Republicans in either chamber must pass if they are to achieve the party's top goal of overhauling the tax code.

Because it is the only measure that can use special rules to circumvent a filibuster by the Democrats, the GOP will add the tax reform plan to the budget resolution to enable passage in both chambers with simple GOP majorities.

"The budget is still the key that unlocks any of these great ideas," House Budget Committee Chairwoman Diane Black, R-Tenn., reminded lawmakers last week when Republicans unveiled their tax reform plan.

Majority Leader Kevin McCarthy announced the House will vote on the budget resolution next week. He touted the provisions in the plan, which includes money for the southern border wall President Trump promised during his campaign.

"Our Republican budget will balance within 10 years, provide money for the border fence, eliminate burdensome regulation and crack down on waste, fraud, and abuse," Majority Leader Kevin McCarthy, R-Calif., said Thursday. "Passing this budget will also enable tax reform, which is the key to economic growth and seeing that Americans take more and more of their hard-earned dollars."

The budget has long been a divisive measure for the GOP, and this year is no exception.

House GOP leaders this summer put off a vote on the budget plan because they lacked enough support within their own party to pass it.

The House plan, which capped spending at $1.13 trillion, made aggressive domestic and mandatory spending cuts while boosting military spending. Moderate Republicans said the cuts were too drastic, while conservatives wanted more reductions.

Conservatives also balked at approving the budget until they could see the actual tax plan that GOP leaders plan to hitch to the measure.

Skeptical GOP lawmakers said they wanted to ensure the tax proposal followed House Speaker Paul Ryan's plan to cut the corporate tax rate to 20 percent, or Trump's proposal to slash corporate taxes to 15 percent.

The GOP plan unveiled Wednesday adheres to the Ryan "Better Way" tax cut proposal for corporations, proposing the 20 percent rate.

"It's all good," Rep. Dave Brat, R-Va., said when asked whether he would back the budget resolution. "I've been pretty clear, you show me Paul Ryan's Better Way Tax plan, or Trump's tax plan, I'm a yes."

Senate Republicans are also preparing a budget resolution.

Senate Majority Whip John Cornyn, R-Texas, told the Washington Examiner the Senate Budget Committee will consider a 2018 resolution next week.

"We are going to do the budget markup in committee next week, then it will come to the floor following that, then we will turn to mark up of the tax bill in the Finance [Committee]," Cornyn explained.

Details of the Senate budget bill have been scarce. Among the unanswered questions is whether the Senate plan will include key priorities Trump included in his own fiscal 2018 proposal, such as a provision allowing the sale of leases for oil and gas drilling in the Arctic National Wildlife Refuge.

"Whatever we can get a majority of senators to support," Cornyn said when asked about Alaska drilling. "That is going to be important."

Senate Republicans have a much slimmer majority than the House. They control 52 votes and can afford to lose only two GOP lawmakers if they hope to pass the resolution with Vice President Mike Pence casting a tie-breaking vote.

Key Senate Republicans on the budget panel have so far come to a tentative agreement on the budget that would allow $1.5 trillion in tax cuts over the next decade.

But there are likely to be significant differences in the House and Senate budget plans, which Republican leaders anticipate will have to be worked out in a conference between the two chambers.

The House budget resolution, for example, calls for $203 billion in cuts from mandatory programs. Moderate GOP senators would likely reject any mandatory cuts.

"It would be disingenuous to suggest $203 billion worth of mandatory spending cuts will make it into the Senate budget," said Rep. Mark Meadows, R-N.C., who is head of the conservative House Freedom Caucus. "So, it will have to be worked out in conference and a compromise will have to be worked out."

Meadows appeared resigned to accept that the House budget's more aggressive spending cuts would likely have to be sacrificed if the larger goal of tax reform stands any chance of passing in the Senate.

"The $1.5 trillion that they have in the Senate budget allows for us to be very aggressive on tax cuts, and I support that," Meadows said.

Robert King contributed to this report.