Sen. Mike Folmer, the Lebanon County Republican who sponsored the initial legislation and has been among its biggest champions, is now considering pressing for changes and another vote by both chambers instead of signing off on the House bill and sending it to Gov. Wolf.
"There have been lots of discussions - but there's been no decision," Folmer's chief of staff, Fred Sembach, said Thursday.
Sen. Daylin Leach (D., Montgomery), the bill's cosponsor, said trying to again revise it could spell disaster.
"If we send it back to the House, we may never see it again," said Leach, who said he prefers that the Senate accept the House bill and iron out any flaws through the courts and the regulatory process.
Supporters had hoped last week's House vote marked their final hurdle. Gov. Wolf even congratulated advocates - many of them parents of children with chronic illnesses - who for years had lobbied legislators to make Pennsylvania the 24th state allowing patients to access medical marijuana.
The law would establish a licensing, dispensary, and regulatory system, and make the drug available in pill, oil, or ointment form to patients who suffer from cancer, epilepsy, multiple sclerosis, seizures, and other conditions.
Wolf's spokesman, Jeff Sheridan, said the governor "was ready to sign the House bill and had hoped it would pass quickly through the Senate."
But when the Senate reconvened this week and the bill did not come up for a vote, concern sprouted.
Senate staff and lawyers have flagged a number of "flaws," such as reference numbers between the two bills not lining up and language that would make applications of the law difficult if not impossible in some ways.
For instance, Leach said, the House bill would require that no marijuana dispensary operate within 1,000 feet of a school in Philadelphia. That would make it difficult to open one in Center City, he said.
Another issue, flagged by Folmer's staff, is imprecise language about the regulation of marijuana growers, processors, and dispensers. The Senate bill referred to "license" - a word struck by the House in favor of "registration," Sembach said.
Even technical flaws could mean roadblocks to getting the system up and running properly for the patients who need it, Sembach said.
"This would be like giving a child a toy at Christmas but then not giving a battery to make it work," he said. "It's too important to enact a bill into law that may not work."
After an advocate this week posted questions to him on Twitter, Sen. Majority Leader Jake Corman (R., Centre) announced that lawmakers would vote on the bill the week of April 4. "Technical issues w/ the bill being reviewed," Corman tweeted.
His spokeswoman, Jennifer Kocher, said Thursday that there was "no poison pill in the bill" but that Corman would follow Folmer's lead on how to proceed. "We are not saying this is dead," Kocher said.
One advocate, Lolly Bentch Myers, said she met daily with lawmakers this week to discuss the next steps.
"We're getting a lot of conflicting information about whether the Senate will concur or not," said Myers, a Dauphin County mother who founded Campaign for Compassion because her 8-year-old daughter, Anna, suffers from debilitating seizures. "There's so much tension right now and a lot of arguing back and forth."
For Leach, the uncertainty is a concern. For six years, he has sought such legislation, only to be rebuffed time and again. It would be wrong, he said, to risk losing an otherwise "very good bill" by exposing it to the caprice of the House.
"Perfection is the white whale of government," Leach said. "You're always chasing it; you're never catching it."