Senators met for a rare Monday session and talked behind closed doors about a plan to gradually increase the 19-cents-a-gallon gas tax to 43 cents by 2018, assuming prices stay flat.
The tax is part of a plan to raise $1.5 billion more per year for roads.
It's the third-straight voting day that senators haven't voted since they amended a House road-funding plan May 21. Lawmakers may adjourn next week for the summer.
Some Republican senators opposing the gas tax hike prefer asking voters to increase Michigan's sales tax from 6 percent to 7 percent, dedicating the extra revenue to roads. That would require approval from two-thirds of state lawmakers.