The Mohegan Sun Exposition Center is moving along.

Mohegan Sun officials will mark a milestone in the center’s construction Monday, hosting a topping-off ceremony, in which a crane will hoist the last structural beam into place. The beam will bear the signatures of ironworkers, Mohegan Tribal Council members and guests, according to the tribe.

The $80 million, 240,000-square-foot center is scheduled to open next June, in time to host the 3rd annual Barrett-Jackson Northeast Auction of collector cars. The first two auctions in the series have been held in Mohegan Sun Arena, drawing large crowds.

In keeping with tradition, the final beam will be topped by a small evergreen tree as well as the Mohegan, U.S. and Connecticut state flags.

Speaking at a groundbreaking for the project in March, Kevin Brown, the Mohegan tribal chairman, said the center, when complete, would provide some 300 permanent jobs, bringing the number of Mohegan Sun employees to more than 7,000.

With the center, Mohegan Sun officials expect to be able to compete with venues in Boston and New York for trade shows and conventions.

— Brian Hallenbeck