In 1992 the Swedish Work Environment Authority (SWEA) considered actions limiting the permitted working hours in forest machine operation. As the forest harvesting industry collectively took initiatives aiming at improving the work environment, SWEA agreed to postpone their actions during two years. The forest industry corporations, the forest machine contractors’ association, the trade unions, SWEA, and researchers acted together to manage improving activities. After the two years respite, the Work Environment Authority only issued recommendations. The industry actors did not agree on how to continue; hence the initiatives were closed down. Evaluations have shown that several problems still remain. No more comprehensive collective action has been taken against the work environment and occupational health problems in the industry. However, when discussing issues of work environment and occupational health with mechanised forest harvesting contractors and forest machine operators, they still often refer to the initiatives in the middle of the 90’ies. At least the initiatives were successful in raising the awareness among contractors and operators. My aim in this paper is to discuss why the collective initiatives succeeded in raising the awareness among mechanised forest harvesting contractors and machine operators. I do that by analysing documents on the initiatives together with new qualitative interviews with the most central actors who worked on them. I show how the threat of working time regulation caused a shock in the organisational field which made opportunities for collective action aiming at institutional change. The shock caused by the governmental authorities de-stabilised the organisational field and opened it up for changed norms and rules. Once new norms and rules had been established, the field was stabilised and re-institutionalised. The results show how the acting of institutional entrepreneurs may have long term and unforeseen impact in changing the norms and perceptions of other actors in the field as well as for policy.