House Assistant Majority Leader Byron Rushing could face a primary challenge this fall.

Jon Santiago, a Boston Medical Center emergency medicine resident and Ward 4 committee member, filed to run for the Ninth Suffolk seat Monday.

Rushing, a veteran South End Democrat, has represented the Ninth Suffolk District, which includes most of the South End and stretches from the Fenway and Back Bay into Roxbury, for over 35 years. Rushing has received the paperwork to run for reelection, according to a state elections office spokeswoman.

Rushing holds the fourth highest rank among Democrats in the House of Representatives and is one of the most senior members. He is one of two people of color in House Speaker Robert DeLeo's leadership team. The 75-year-old Rushing was first elected to the House in 1982.

Neither Rushing or Santiago were immediately available for comment.