Primary school teachers are being warned in paid union meetings this week that their latest pay offer paves the way for the Government to introduce performance pay.
Their union, the Educational Institute, says the teachers need to use the pay round to fight the Government's education policies.
The institute says the proposed change is part of a global trend its members should resist.
The institute's general secretary Paul Goulter says good faith bargaining requirements prevent him from revealing details, but the offer will make it easier for the Government to introduce performance pay in the future.
"The direction the Government is trying to head the bargaining in is about laying the platform for a subsequent introduction of performance-based pay," he says.
"We don't think that's at all appropriate; we also know that performance-based pay is bad for education-based systems like ours. The OECD also has that view."
The secondary teachers' union, the Post Primary Teachers Association, is also holding paid union meetings to discuss their pay offer.
It says performance pay does not feature in the ministry's offer, but its members are not happy with government policy either.