A statement said: "Having considered this very carefully, we see no advantage to our members. However, if the institute wishes to enter into discussions with the association about the possibility of establishing a new Scottish teachers' union with a federal structure, we would be willing to participate on that basis."
Schools are being sent a letter emphasising that the association "remains the independent voice of secondary teachers".
Disgruntled secondary members split from the EIS in 1944. There have been three attempts to re-establish the liaison, the last 20 years ago. The SSTA accepted a federal structure but the EIS conference threw it out.
David Eaglesham, the SSTA's general secretary, said the union, with around 6,500 members, would talk to the EIS, which has around 49,000, if the interests of secondary teachers could be protected within a federal structure. Pre-five, primary, secondary, further and higher education teachers and lecturers would have to be in distinct sections. Mr Eaglesham said the association was under no financial pressure to merge.
Ronnie Smith, the EIS's general secretary, welcomed the SSTA willingness to talk but felt it unlikely that such preconditions could be met. "I believe, as I think do many teachers, there is a strong case for professional unity," Mr Smith said.