A government ban on gay Pride events this weekend in Budapest has put Hungary’s right-wing strongman, Prime Minister Viktor Orban, in a tricky spot.

Mr. Orban’s party in March rushed legislation through Parliament that made it illegal to hold gatherings like Pride parades, under an earlier law banning material that “propagates” homosexuality.

Billed as an effort to protect children, it looked to politicians and analysts like a trap set for Hungary’s surging opposition leader, a conservative whom Mr. Orban hoped to expose as a closet liberal soft on child protection. Instead, it may be Mr. Orban who is ensnared.

Despite the ban, the Budapest Pride parade is set to go ahead on Saturday, recast by the capital city’s liberal mayor, Gergely Karacsony, as a municipal event celebrating Hungary’s recovery of full freedom when Soviet troops pulled out in June 1991.

Tens of thousands of Hungarians and foreigners, including more than 70 European Parliament members, are expected to join a parade renamed as Budapest Pride Freedom. The mayor said that thanks to the government ban it would likely be Hungary’s biggest-ever Pride parade. He predicted a turnout of at least 50,000 people.

Mr. Orban and his governing Fidesz party now face a choice: try to enforce their ban and punish participants, or let the march go ahead and risk looking impotent.