The main tenant has not evenly divided the unit. Are there any legal actions I can take as a subtenant?

We recently established a new tenancy agreement that legally recognizes my name as a subtenant in the document. However, there is a significant issue regarding the distribution of rental costs. Currently, the main tenant has unilateral control over determining the amount we, as subtenants, are required to pay for the unit, without any prior agreement or fair division of expenses.

From my calculations, it appears that the subtenants are effectively covering the entire rental payment, while the main tenant is contributing nothing toward the rent. This situation raises concerns about fairness and transparency in our rental arrangement. I am considering exploring potential legal actions to address this issue, as it seems unfair for the subtenants to bear the full financial burden without proper agreement or compensation from the mainp tenant. What are my options in this situation?