A Swansea comprehensive was closed on Wednesday when members of the National Union of Teachers staged a one-day strike in an escalating row over responsibility payments.
Further strikes are planned at two other city secondaries and a primary school in Ebbw Vale, over the replacement of the old management allowances with teaching and learning responsibility points (TLRs).
Gowerton comprehensive closed its doors to all pupils apart from sixth-formers as teachers staged their second strike at the school. The first was in July.
The union claims a number of teachers have lost sums ranging up to pound;5,600 each as a result of restructuring.
David Evans, NUT Cymru secretary, said: "Our members remain strong on this.
We have had talks with the head and governors and we remain committed to finding a solution. But the new structure has already been imposed."
Head Paul Green said: "The restructuring took place in line with the guidance. Nobody is losing their jobs but there are some people who will be financially disadvantaged - but it must be the same in every school.
"We have met with the union but unless its position alters, I would not be optimistic."
Two other comprehensives in Swansea may also take action. At Penyrheol, NUT members have voted for strike action this month. Teachers could also walk out at Cefn Hengoed before Christmas, following an earlier strike in July.
And as TES Cymru went to press, talks were taking place between the NUT and governors at Blaenycwm primary, Ebbw Vale, to avoid a strike there next week.
Mr Evans said the union was prepared to go to the conciliation service ACAS. But he raised concerns about the concentration of TLR-related problems in Swansea.
"We are worried about the advice the LEA sent to schools on the new structures," he said.
A Swansea council spokesperson said it had worked with all the trade unions on workforce remodelling and collaborated with other authorities on guidance.