Often at this time of year, it becomes necessary to note something about public-school teachers’ strikes — they’re illegal.

Teachers unions are not supposed to go on strike, hurting students. But in a number of Rhode Island communities this year, that is exactly what has happened.

This annual ritual at the start of the school year is one of the ways unions put pressure on local officials to fold during negotiations. (That is why many teachers’ contracts are timed to expire at the end of August, for maximum uncertainty, cost and inconvenience for local officials, parents, students and, indeed, the general public.) Parents are eager to get their children back in school, and when schools are unpredictably closed, they get angry at their elected officials, pressuring them to “do what it takes” to get the schools back in session again.

State law recognizes that this sort of education blackmail is not in the public interest. The problem is that the law goes essentially unenforced. Sometimes, it takes a judge, after days or weeks of petitions, to step in and order the teachers back to work.

Since striking tends to reward the unions, they naturally continue to thumb their nose at the law. A Rhode Island law setting a steep monetary penalty for each day teachers refuse to report for work would be one way to curtail this abuse.

This year, negotiations have been particularly tough. School committees face increasing budgetary pressures, making it difficult to give away the store as in the past. A new state law tends to limit how much communities can hike property taxes in any one year. And the General Assembly passed a budget this year that failed to boost education aid.

Teachers in Rhode Island are already among the most highly compensated in America, both in pay and benefits, though performance in Rhode Island public schools has been mediocre by many measures, especially when compared with other Northeast states, for several reasons. To a large extent, that is a result of negotiated contracts. Teachers have been rewarded more for seniority and certain academic degrees than merit, and administrators often have their hands tied in trying to improve things. Students, obviously, are the ones who most suffer as a result.

Teacher strikes help stack the deck against the public. They are illegal for a good reason: They hurt students by undermining public education. And they set a bad civic example. They are one back-to-school ritual the Ocean State can do without.