BUCHAREST, Romania — The European Union’s highest court began examining a case on Tuesday over a Romanian man’s attempts to get legal residency for his American husband, a closely watched hearing that will have major implications for the legal recognition of same-sex relationships across Europe.

The case, legal experts say, could determine whether same-sex partners are afforded some of the same benefits and rights available to heterosexual spouses across the 28-member bloc, irrespective of the countries’ stance on same-sex marriage. Specifically, it would affect whether they would be allowed to live and work freely across the European Union, one of the region’s fundamental principles.

“This is the first time the European Court of Justice has been asked to decide whether ‘spouse’ includes a same-sex spouse,” said Robert Wintemute, a professor of human rights law at King’s College London.

The case before the court involves Adrian Coman, a Romanian rights activist, and his American partner, Claibourn Robert Hamilton. The couple were married in Belgium in 2010, seven years after the country legalized same-sex marriage. Belgium is one of 13 countries in the European Union to allow same-sex marriage, while a further nine member states have civil unions or something similar, according to Mr. Wintemute.