Teachers across Scotland still haven't received 9 months worth of backdated pay.
Union bosses say some local councils are yet to compensate school staff after a 1.5% salary increase was agreed earlier this year.
Glasgow city council is among the employers yet to award the money.
EIS General Secretary Larry Flanagan said: "It is disappointing that a number of Scottish local authorities have been slow in arranging for the 2015 pay settlement to be applied to teachers’ salaries.
"Negotiations on the pay and conditions agreement were concluded in early September, and the EIS opened a ballot of its members in that same month. The ballot result – an acceptance of a 2-year offer totalling 2.5% – was announced in early October.
Now, more than two months later, many teachers are still awaiting their local authority employers implementing the nationally agreed pay increase of 1.5% for this year
"Teachers’ pay settlements apply from the start of April, so Scotland’s teachers and associated professionals are now due some 9 months of backdated pay increase. Sadly, the slow response from some local authorities means that many teachers will not have received this payment before Christmas.
"While some authorities have been quick to make the backdated payments, and others have pledged to do so in December or at least in time for January’s credit card bills, the indications are that some local authorities will be dragging the process on for months to come.
"The most extreme case the EIS has heard so far is that at least one authority will not be making these payments until March 2016 – for a pay award that applies from April 2015 and which was formally agreed in October this year. This is simply unacceptable."