Speaker Nancy Pelosi plans to invite NATO’s secretary general to address a joint session of Congress in April to mark the 70th anniversary of the alliance, according to a source familiar with the planning.

Jens Stoltenberg, NATO’s top official since 2014, has never addressed a joint session of Congress. But Pelosi’s (D-Calif.) invitation — the first of her speakership — comes at a perilous time for the United States’ relationship with NATO.