From Longman Business Dictionary
work-to-ruleˌwork-to-ˈrule British EnglishBrE, work-to-contract American EnglishAmE noun [singular]HUMAN RESOURCES an occasion when people protest about a situation at work by doing their job less quickly or effectively, but without breaking their employer’s rules or the terms of their contractThe work-to-rule exposed the chronic staffing problems in the emergency services.
→ see also work to rule under work1