Britain's Supreme Court will rule Tuesday on whether the prime minister or Parliament has the right to trigger the process of taking Britain out of the European Union.

The 11 justices will either uphold an earlier ruling giving Parliament a direct role in invoking Article 50 of the EU's Lisbon Treaty or reject that ruling in favor of the government's claim it can do so without a vote in Parliament. Article 50, which has never been used before, starts the formal process of taking Britain out of the 28-nation EU. Here are answers to some key questions about the case.

Prime Minister Theresa May has pledged to start the Article 50 process, which is expected to last two years, by the end of March. European leaders want to get talks underway, and some British voters who backed Brexit in a June referendum are getting impatient.

Having Parliament play a direct role could slow the process down. Although the leader of the opposition Labour Party says its legislators will back Brexit out of respect for the referendum result, the process could easily be delayed in the House of Commons or the House of Lords.

May's ministers have prepared several draft pieces of legislation that could be introduced in Parliament. The goal is to craft a very short, limited bill that would give May the authority to invoke Article 50, but would be difficult to amend or tamper with.