The NASUWT has accused its fellow teaching unions of "feeding the Government's propaganda machinery" by balloting members on strike action over pensions before formal negotiations with ministers have concluded.
More than 300,000 NUT and ATL members this week received their ballot papers, but the NASUWT has yet to announce whether it will hold a ballot.
General secretary Chris Keates said she was waiting for the outcome of talks between the TUC and the Government before showing her hand.
In a letter to The TES, Ms Keates said her union was "under no illusions" of the "inevitability of strike action", barring a "radical" shift in the Government's position.
"However, we have no intention of feeding the propaganda machinery of this Government by enabling it to claim that unions are not serious about negotiation," she added.
NASUWT members are "demonstrating the sound common sense of the teaching profession", Ms Keates added, by waiting for the talks to finish before resorting to industrial action, "to avoid derailing negotiations and giving ministers the excuse to impose the changes".
But Ms Keates called on all unions to join forces on the issue. "Never before has unity of purpose across the entire trade union movement been needed to protect the workforce," she said.
She added that the NASUWT already had a mandate from its 2010 conference to ballot members on action against pension changes where necessary.
The NUT and ATL ballots - of all members eligible for the teachers' pension scheme - will come to an end in mid-June. Union leaders will then decide whether to press ahead with the first strike, expected later that month. Further strikes could take place in the autumn term.
Writing in this week's TES, ATL general secretary Mary Bousted said: "Very few teachers or lecturers, and certainly no ATL members, like the idea of a strike.
"I am prepared to take part in any discussions which could lead to suspending strike action. All I need is the gun removed from my head, and a significant demonstration of willingness to compromise."
A Department for Education spokesman said: "We are clear that a strike by teachers will achieve just one thing: disruption to pupils' learning."
Comment, page 25; Letters, page 28
The NASUWT has lodged a legal challenge with the High Court against calculating pensions using the generally lower Consumer Price Index, instead of the Retail Price Index.
The switch, which the union claims will cost an average teacher #163;50,000 over 20 years, was introduced without consultation.
Other unions involved in the challenge include the Fire Brigades Union, the Prison Officers Association, Unite and civil servants' union PCS.