Earlier this week, members of the Educational Institute of Scotland (EIS), the country's largest teaching union, voted against moves to give councils more control over the amount of time they spend teaching.
They also rejected plans to water down a list of set tasks they are protected from doing.
However, the Scottish Secondary Teachers' Association (SSTA), which represents some 10,000 teachers, has reiterated its support for the changes, saying they did not constitute a threat to the working environment.
Alan McKenzie, the SSTA's acting general secretary, said: "Our annual congress of 2013 had accepted the recommendations.
"Congress did not regard these changes as representing a deterioration in conditions of service. The view expressed was that they were measured and reasonable."
At a meeting yesterday of the Scottish Negotiating Committee for Teachers (SNCT) - which includes unions, council leaders and the Scottish Government - the EIS stated its opposition.
A spokesman said: "The EIS, and all other parties on the SNCT, will now consider their positions and have agreed to hold further discussions ©in the near future."
A spokesman for Cosla, the umbrella organisation for councils, added: "Our position has not changed."