Members of the Legislature should tread carefully when considering plans to overhaul Maine’s tax system.

A plan floated this week by the two chairmen of the Taxation Committee, Sen. Joseph Perry and Rep. Richard Woodbury, has troubling elements.

First, the proposal would greatly expand the application of the state’s sales tax while lowering it to 4 percent. Currently, the rate is 5 percent. That doesn’t sound so bad, except the tax would be applied to such essentials as groceries.

Second, the plan would create a flat income tax of 6 percent. Maine essentially has a flat tax now. Because the highest rate – 8.5 percent – kicks in at about $18,000 of yearly income, much of the progressivity of the income tax system evaporates. A flat tax would make the problem worse, although the legislators hope that a generous earned income tax credit and other safety valves could protect low-income workers.

Shifting the state’s tax burden from the income tax to the sales tax creates an added burden on families with limited resources. It would increase the percent of their income that goes to pay taxes, while earners with the highest salaries would get a break.

Ideally, any restructuring of Maine’s system should improve the progressivity of the income tax by expanding the lower brackets so fewer workers are captured by the top rates. A broadening of the sales tax and new levies on discretionary products like alcohol and tobacco might provide the necessary revenue, but there shouldn’t be a sales tax on groceries. While the plan is intended to be revenue-neutral, it’s hard to see how the income and sales tax can both go down without creating a new budgetary hole.

Perry and Woodbury deserve credit for starting the Legislative conversation on tax restructuring, but a lot more talk is needed.