BELGRADE, Wednesday—The Serbian Education Union has turned down a ten per cent salary raise offered by the government yesterday, describing it as unacceptable. The union committee said today that teachers would continue their industrial action as yesterday's offer did not address its demands. Other unions have threatened a complete withdrawal of labour unless a new salary is agreed on by February 18. At present, teachers in about half of Serbia's schools have reduced class times from 45 to 30 minutes in support of their claims.