Australia’s highest court has set a date for a full hearing into how a group of purportedly Sri Lankan asylum seekers were detained at sea, a case that will test the Australian government’s authority to pursue its immigration policies.

Reuters quotes a lawyer for the group of asylum seekers as saying it was likely the United Nations would seek to join the case, a highly unusual step, they said showed the level of international concern over Australia’s “Operation Sovereign Borders”.

Justice Kenneth Hayne, who has said the case appeared to be unique in the world and raised serious questions about how far Australian power extends, set an expedited two-day hearing before a full bench of the High Court for October 14 and 15.

The boat carrying the 157 asylum seekers was intercepted in late June and held by Australian authorities at sea for weeks. The group’s lawyers argue that the their detention and the government’s plan to send them to Sri Lanka or back to India, from where they had left, were illegal.

The fate of the group has highlighted Australia’s immigration policy, in which boats carrying would-be asylum seekers are intercepted at sea and turned back.

Reuters reports that the U.N. would not be a direct party to the case but could offer legal opinion, testimony and text evidence.