Italian to English Law/Patents Human Resources Court Judgment

The context is a court judment on the issue of unfair dismissal from employment. There is a section on the calculation of severance pay and the court indicates all forms of compensation which should be considered for the severance pay computation, one of which is the pay in lieu of notice. In this context, there is the following paragraph:

"Essa (l'indennita sostitutiva del preavviso) va assoggetttata alla normale contribuzione e, per l'intero periodo cui si riferisce, comporta la maturazione del trattamento di fine rapporto..."

I can't understand the meaning of assoggettata in this sentence. Any suggestions would be greatly appreciated !!

Thanks !