Hundreds of teachers blocked the busy National Highway No. 1 (NH-1) near Ludhiana on Sunday after the Punjab government failed to give them any assurance on their demand, leaving hundreds of vehicles stranded.The teachers, belonging to different teacher organisations under the banner of Punjab Joint Front of Teachers (PJFT), had gathered here on Sunday for a protest rally, to oppose the state government's move to fix their salary for first three years at the basic pay of just over Rs 10,000 per month and demanding that they be given the full salary as per the pay scale.The protesting teachers had set a 3 p.m. deadline for the Congress government in Punjab, led by Chief Minister Amarinder Singh, to address their demands."We cannot accept this move of the Punjab government to force us to take only the basic salary. We will not stop this agitation till the Punjab government budges on its stand," a teacher leader told the gathering.According to sources, over 10,000 school teachers had gathered here for the protest rally.Police and district authorities had put up barricades to prevent the teachers from reaching the highway but the agitated teachers broke through the barriers and blocked the highway.Police tried to use mild force to stop the protesters but were unsuccessful.