The Hawaii State Teachers Association now is arguing that its acceptance of random drug testing among its members could be challenged on constitutional grounds and is pressing for a procedure that limits the testing to a subset of employees for whom there is "reasonable suspicion."

In other words: The union is going back on its agreement.

Hawai'i public schools face so many other, more critical challenges, so it is beyond belief that this dispute is dragging on this long after the contract was ratified in June 2007.

The means of determining who meets the "reasonable suspicion" test is still under negotiation. But whatever the system, there's no way such a limitation could be considered random by any rational definition of the word.

And random drug testing is what the union agreed to in its signed two-year contract, which gave the membership substantial raises.

HSTA Executive Director Mike McCartney is right about one thing: This is an issue that almost certainly will be argued in the courts. But there's no guarantee that the HSTA's proposed "reasonable suspicion" alternative will withstand legal scrutiny while random testing won't.

So far, said Attorney General Mark Bennett, there's been no case within the Ninth Circuit, including Hawai'i, that clearly settles whether drug testing can be a contract provision that's accepted through the collective bargaining process.

Even so, the HSTA, which collectively bargained for that provision as part of a package the membership ratified, has no excuse for withdrawing its acceptance now.

Teachers accepted that testing undoubtedly because of the contract's other key provision: pay increases of up to 11 percent over 18 months.

Those salary hikes have largely been implemented; now it's time for the teachers' union to fulfill its end of the bargain and enable truly random testing to begin. The original implementation deadline, June 30, is long past.

The state administration has played a part in the deteriorating rhetoric, with its threats of rescinding pay raises and hard-line approach to the June 30 deadline, resisting a call for extensions.

But given the HSTA's recent effort to dodge its agreement, the state's formal complaint with the Hawai'i Labor Relations Board seems reasonable.

In the complaint, the state Office of Collective Bargaining charges that the union has failed to negotiate terms of the testing program in good faith. The HSTA's 11th-hour turnabout certainly seems to provide supportive evidence.

The union will have 10 days to submit a response to the complaint. What it should do in that time is fulfill its original commitment.

The time for the HSTA to raise its constitutional objections was more than a year ago, when the two-year contract was being hammered out.

If it so chooses, the union will have a chance to put the issue back on the table when negotiating the next contract.

Collective bargaining rests on a foundation of trust, and rescinding a previously bargained and ratified provision undermines that trust.

The union agreed to the random tests; its membership accepted them. It's time to implement them and move on to more important issues, like educating our children.