Massachusetts legislators, toiling in secret to finalize a rewrite of the voter-passed marijuana legalization law, hit an impasse Thursday as they triedto iron out differences between a House version that would alter major parts of the ballot measure and a Senate bill with more modest changes.

“We’re stalled and we’re done for the night,’’ said Representative Ronald Mariano, the House majority leader and a top negotiator on the bill. “We haven’t scheduled a meeting for tomorrow.’’

Supporters fear that a significant delay could thwart the expected opening of retail stores, aimed for July 2018. Lawmakers had hoped that a final recreational marijuana bill could be voted on by all lawmakers on Friday and sent to Governor Charlie Baker’s desk by the Legislature’s self-imposed deadline of Friday night.

If lawmakers can find common ground, their bill would answer key questions about the future of legalization in the state. Here are six.

What’s the pot tax?

Last year’s ballot measure, Question 4, put in place a relatively low state tax on marijuana purchases: 3.75 percent. In addition, the measure gave cities and towns the right, though not the mandate, to append an additional 2 percent tax that they could keep. When you add those to the state’s 6.25 percent sales tax, the maximum tax on marijuana purchases would be 12 percent, or $12 on a $100 pot brownie purchase.

According to rough estimates from the state Department of Revenue, that tax on recreational marijuana could generate a total of about $65 million in revenue in the first year of sales and about $130 million in the second.

That’s a significant sum. The state pot tax alone would more than cover the expected costs of regulating the industry, experts say.

The Senate bill would leave the tax scheme as is — as approved by voters.

The House bill would ramp up both the state tax and the local tax, and make the local tax mandatory. With the state sales tax, the total pot tax rate would be 28 percent, or $28 on that $100 cannabis brownie purchase.

Senate leaders balked, saying that rate would ensure the black market remains, with people buying from dealers on the street and paying no tax at all. But top House officials said a 28 percent total tax would put Massachusetts in the middle of the pack with other legalization states and bring in enough money to cover not just regulation, but also more drug education and addiction treatment.

Who can ban local shops?

The ballot question, passed by 1.8 million voters, gave voters in each city and town the power to ban retail marijuana stores, farms, infused-product manufacturers (think: pot-infused candy makers), and testing facilities. It also required a referendum if residents in a particular community wanted to sharply limit the number of such facilities in a city or town.

The Senate version would clarify the procedures for such votes, but leave the power with residents.

The House version stripped residents of such power, instead giving it to local officials — something a key municipal group called common sense.

“The House approach is much more desirable because it fixes significant flaws in Question 4,’’ said Geoffrey Beckwith, who leads the Massachusetts Municipal Association. “If the language goes forward as proposed in the Senate version or in Question 4, it will actually delay the rollout of the industry and create ongoing confusion.’’

Who will appoint regulators?

The ballot question, as approved by voters, gave state Treasurer Deborah B. Goldberg unilateral power to hire and fire the officials who will oversee the new billion-dollar industry, a three-person Cannabis Control Commission.

But both the House and the Senate bills would rob Goldberg of such autonomy. Both would expand the commission to five people and give the governor and attorney general the power to appoint, too. But there are differences on specifics. For example: Will most of the commissioners be paid or unpaid?

Regulators are “absolutely essential in a tax-and-regulate system,’’ said Andrew Freedman, who served as Colorado’s pot czar for three years and now runs a cannabis consulting firm focused on good government oversight and responsible industry practices.

Regulators will determine the success of the new industry. They will make rules on everything from signs in pot shop windows to the font size of warning labels on marijuana-infused cookies.

The infrastructure they set up will also help attract or discourage criminal activity.

Freedman said they are key to making sure a gray market doesn’t spring up in Massachusetts, in which people would legally grow marijuana and then illegally sell it in another state.

“There’s just a huge economic incentive to shift marijuana out of state,’’ Freedman said. So it’s key for regulators to create a “closed loop or else you are going to see a lot of out of state leakage and criminal activity.’’

Can records of past pot crimes be destroyed?

The Senate bill would allow people to petition a court to destroy records of prior marijuana charges for incidents that are no longer illegal under current law.

Senators argued there’s no reason for past pot offenders to suffer harm, such as being turned away from a job, given that pot is now legal.

The House and the ballot question had no such provision.

Representative Mark J. Cusack, the House chairman of the Legislature’s marijuana committee, argued that a marijuana bill wasn’t the right place for such provisions.

Will the state end the right to grow and possess weed?

Almost certainly not. Both the House and Senate bills leave in place the right of adults 21 years of age and older to homegrow, buy, transport, possess, and use limited amounts of marijuana.

Will Baker sign the bill if he gets it?

Probably. He’s expressed openness to changes to the ballot question to protect public health and safety. But Charlie Baker ran on an oft-repeated promise not to raise taxes and has been careful not to box himself in, saying the tax rate should reflect the cost of implementing the new law, along with any secondary costs associated with adult-use pot.

“Governor Baker appreciates the Legislature’s careful consideration of the new marijuana law and will review the final legislation that comes to his desk,’’ said communications director Lizzy Guyton.

Baker, a Republican, will have 10 days to review the final bill if and when the Democrat-controlled Legislature sends it to his desk.

If the Legislature is unable to come to a compromise on its rewrite, the ballot question will remain in place.

Joshua Miller can be reached at joshua.miller@globe.com.