TIVERTON — In a straw poll, 144 teachers — three quarters of the union membership — indicated their disapproval of a two-year contract proposal from the School Committee that the union president says would eat up virtually all the raises with stiff hikes in out-of-pocket health-care costs in the second year.

Amy Mullen, the union president, said the committee’s proposal in the second year would mean $3-a-week raises to teachers with at least 10 years’ experience — slightly more than half the membership.

The remaining teachers, who are still working their way up the experience ladder, would come out at least $1,300 ahead in the second year, Mullen said.

But she called the committee’s two-year offer “extremely unreasonable” in comparison to other recent settlements with public school teachers elsewhere in Rhode Island.

Most recently, neighboring Portsmouth reached a one-year agreement beginning next fall that gave the most experienced teachers 3.1 percent raises and net gains ranging from $1,900 to $3,000 for most of the others.

Although that community must still identify cuts necessary to balance its budget, it did not ask teachers to raise their contribution to health insurance, which now stands at 10 percent of the cost of the premiums.

The Tiverton School Committee is offering 2.5-percent raises to teachers on the job at least 10 years come next fall, as well as 1-percent cost-of-living allowances to those still working their way up the experience ladder.

But it is also asking that teachers pay 18 percent of the cost of health insurance, or $2,676 for a family plan.

Last night, School Committee Chairwoman Denise deMedeiros said the committee has offered all it can afford. In the meantime, it has sought nonbinding arbitration, which is scheduled for the first week of May.

Last week, the School Committee passed on a union proposal for a one-year agreement that would have granted 3-percent cost-of-living increases, but conceded a jump of $522 in the employee share of a family health insurance plan, to $1,662 from $1,100.

The one year-agreement would have been retroactive to the expiration of the most recent agreement at the end of last August.

DeMedeiros says the committee favors 2.5 percent raises, along with one-time stipends of $500 for each teacher in the first year of a two-year contract.

While the combination of the two is equivalent to 3 percent, it would not add quite 3 percent to teachers’ base pay at the conclusion of the first year.

Since the day after Labor Day, teachers have been working under court order in accordance with the terms of an agreement that expired last August, refraining from extra duties in a job action called “contract compliance.”

DeMedeiros said Mullen has implied that “contract compliance” would somehow affect graduation, among other school activities.

Mullen said the union will not boycott graduation, although teachers can decide individually whether to participate in the rehearsals or attend the ceremony. Either way, graduation will not be affected, she said.

gmacris@projo.com