PHOENIX – The future of an extension of the Arizona transportation tax will reach a critical point Monday when House Speaker Ben Toma of Peoria said he plans to adjourn the legislative session for the year.

Republicans who hold the majority in the Arizona Legislature are working to strike a final deal with Democratic Gov. Katie Hobbs and leaders of cities, counties and tribes in metro Phoenix over an extension of a transportation tax that has funded expansions of the region's freeway and roads system, bus routes and light rail over nearly four decades.

Failure to get a plan out of the Legislature that the governor will sign - and can win support from voters in Maricopa County next year to extend the half-cent sales tax for another 20 years - would affect all of Arizona.

That's because the regional planning agency called the Maricopa Association of Governments funds its own projects outside the state general fund using the sales tax proceeds which will average about $1 billion a year over the coming 20 years. If the tax goes away, transportation projects in the other 14 counties would be competing for limited state transportation dollars with a county that is home to nearly two-thirds of Arizonans.

Toma said the plan is to adjourn for the year Monday with a potential deal on extending Proposition 400 the major item on the agenda.

He and GOP Senate President Warren Petersen, R-Queen Creek, said there’s been progress on settling the Proposition 400 extension but stopped short of proclaiming a breakthrough.

But Sen. Ken Bennett, R-Prescott, said he's been told a tentative deal is in place, but that bill language still needs to be finalized.

"Unfortunately, I can't tell you if we're going to have the deal or not yet, at this point,'' Toma said last week. "We’ve been waiting for a response back from MAG, and my understanding is they're waiting for input from some of their people before they respond to us.''

Getting Toma on board is critical, since new House rules adopted in January by majority Republicans say the speaker must sign off on all legislation before it goes up for a vote.

"The starting point is really they have to bring us back language or something that we can get the votes for - and I guess to be blunt, starting with mine,'' he said. "So, if they can't get my vote, I'm not sure how they're going to get any others at this point.''

Hobbs spokesman Christian Slater declined to comment on the status of negotiations. Neither did a spokeswoman for MAG. Requests for comment from new MAG chair Kate Gallego, mayor of Phoenix, were not immediately answered.