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A search for patterns

At the heart of Halsema’s research lay one fundamental question: “Can patterns and relationships be identified within and between the various sectoral CLA schemes and sectoral pension schemes, and if so, what do these patterns and relationships look like? Furthermore, can they form the basis for a universal model for assessing and determining the applicable scope of sectoral schemes for a (company of a) given employer, thereby reducing the uncertainties and risks associated with their interpretation?”

The answer proved to be yes. From his analysis, Halsema developed a categorical and diagnostic system - in essence, a kind of periodic table of industrial sectors. This forms the basis of a computational model that links legal patterns and relationships to concrete variables. Using data such as the number of employees, their contracted working hours, and total wage costs, the model can determine which sectoral scheme applies.

The importance of legal certainty

This research touches upon the very core of Dutch labour law. Virtually all employers and employees in the Netherlands are affected by sectoral CLAs and pension funds. Many scope provisions are declared generally binding by ministerial decree and published in the Staatscourant (Government Gazette), yet their wording is often complex and open to multiple interpretations. Halsema illustrates how this plays out in practice: “For decades, Dutch lawyers have complained about the interpretative challenges of scope provisions. They speak of ‘the intellectual feats required to choose between two equally defensible decipherings’, of ‘legal conjuring tricks that pull a meaning out of the CLA hat’, of ‘sleepless nights’, and, more recently, of the ‘growing chorus of criticism’ surrounding these provisions.”

Uncertainty in interpretation can lead to lengthy proceedings and substantial financial claims. For instance, an employer who has not joined a sectoral fund may later be ordered to pay up to twenty years’ worth of retroactive contributions. Employees, meanwhile, are generally entitled to pension accrual even if their employer has never paid any premiums. According to Halsema, this demonstrates how vital legal certainty is: “All of this undermines the financial stability not only of sectoral funds but also of employers and employees alike.”

Legal certainty through calculation

The model developed by Halsema works in three steps and uses three central variables: the number of employees, the total number of contracted working hours, and the total wage sum in euros. These allow the calculation of a company’s relative main activity — in other words, its ‘principal work’. Crucially, Halsema argues that economic indicators such as turnover should, in principle, play no role in this assessment: “Given the essential social functions of sectoral CLA and pension arrangements, economic functions should not in principle influence the determination of scope.”

He emphasises that the model is not a ‘magical formula’, but rather a verifiable and reproducible method of assessment: “In essence, determining the correct applicable scope is about the accessibility of information and the verifiable interpretation of that information. Those who possess the right data can make the right judgment.”

From the courtroom to practice

Recent cases, such as Booking.com, Picnic, and Medux, underscore the relevance of Halsema’s research, illustrating how disputes over the applicable scope can lead to complex litigation. The outcomes have direct consequences for both employees and employers. “Would it not be ideal,” Halsema wondered during his research, “if courts, scholars and, above all, practitioners could assess and determine the applicable scope in the same consistent, reproducible way, one that enhances legal certainty?”

His dissertation now provides precisely that: a concrete instrument to achieve such clarity. It can assist judges in their interpretation but also serve employers, trade unions, lawyers, and advisers who face these questions in everyday practice.

Personal motivation

Halsema’s choice of topic was no coincidence. He explains: “During my work as a lawyer, my interest in this subject grew over the years. I thought it would be valuable to develop a scientifically grounded model for assessing and determining the applicable scope of sectoral schemes in a clear and uniform manner. In doing so, I hope to contribute to greater legal certainty.” The PhD journey brought its share of surprises but also a great sense of fulfilment. That his legal research has resulted in an applicable mathematical model, he regards as a remarkable outcome.

Future and impact

For Halsema, the research will have achieved its goal if the model is actually applied in practice and contributes to greater legal certainty. He does not view his PhD as an endpoint but as a new beginning. Plans are currently being explored to publish his dissertation as a book, ensuring that the insights reach a wider professional audience beyond academia. He also envisions regular updates and follow-up studies, with greater attention to the qualitative criteria that shape the scope of sectoral schemes.