They can not do that due to ICANN rules; transfer of domain name must not be hindered by any ICANN members.
Inter-Registrar Transfer
Holder-Authorized Transfers
Registrar Requirements
Registered Name Holders must be able to transfer their domain name registrations between Registrars provided that the Gaining Registrar's transfer process meets the minimum standards of this policy and that such transfer is not prohibited by ICANN or Registry policies. Inter-Registrar domain name transfer processes must be clear and concise in order to avoid confusion. Further, Registrars should make reasonable efforts to inform Registered Name Holders of, and provide access to, the published documentation of the specific transfer process employed by the Registrars.
See the link: https://www.icann.org/resources/pages/transfer-policy-2016-06-01-en
If they do that they will loose many customers and possibly loose trust on namejet also