In a further escalation in tensions with Saudi Arabia, the Iranian government today banned its citizens from making the annual trip to Islam’s holiest city, a journey required at least once in a lifetime for all Muslims financially and physically capable of doing so.

The ban comes near the end of a tense week between the two rivals after Saudi Arabia, a predominantly Sunni country, executed a prominent Shiite cleric on Saturday. (Iran is the largest of the few predominantly Shiite countries in the world.) In the subsequent days, the two countries severed diplomatic relations, Iranian protestors attacked and set fire to the Saudi embassy in Tehran, and today Iran accused the Saudis of bombing its embassy in Yemen.

About 600,000 Iranians contribute to Saudi Arabia’s $18 billion religious tourism industry each year, so the ban could impact the Saudi economy. (The Iranian government also banned all Saudi imports today.) The last time Iran stopped its citizens from making the hajj was in 1987, after 400 mostly Iranian pilgrims were killed by Saudi riot police.