Republicans claimed Monday they made progress on a joint Senate-House conference tax bill over the weekend, but said that the biggest questions regarding the negotiations haven’t been worked out yet.

“I'm pleased with the progress we’re making,” the conference committee chairman, Rep. Kevin Brady of Texas, told reporters Monday evening.

Brady said they were still on schedule for voting on a conference bill next week.

But, Brady and others also indicated they hadn't yet reached conclusive decisions on the big questions facing the conference.

Corporate tax rate

Brady, the chairman of the House Ways and Means Committee, said the negotiators still haven’t locked in a final corporate tax rate. In both the Senate and House versions, that rate was lowered from 35 percent to 20 percent.

“Nothing’s final 'til everything's final,” Brady said.

“Tax reform is truly a Rubik’s Cube, so as we make changes and improvements in one area, there's impacts” on other areas of the bill, he said.

Free-market groups are pressuring Republicans to stick with the 20 percent corporate tax rate, rather than settle for 21 percent or 22 percent in order to free up revenues to devote to other tax breaks that could win the votes of wavering members.

Corporate AMT

The Senate bill added the corporate Alternative Minimum Tax back into the plan just before passage as an offset for other tax breaks demanded by some GOP senators. But, its inclusion has drawn significant opposition from businesses. Republicans, like Sen. Chuck Grassley, R-Iowa, identified it Monday as a problem that would have to be fixed in the final bill.

But Republican Sen. Orrin Hatch of Utah, the chairman of the Finance Committee and a conference member, said a solution has not yet been found. “We’re not that far along,” he said.

Individual mandate

The Senate version of the bill included repeal of Obamacare’s individual mandate, while the House bill did not.

Brady said he was waiting to see how the Senate might work on side deals to lower insurance premiums, bills that might be necessary to ensure a “yes” vote from Sen. Susan Collins, R-Maine.

On Monday, nearly 70 House Republicans signed onto a letter calling for repeal of the mandate in the tax bill.