The current hotel labor contract, which was completed two years ago, called for the construction of a health care center for the workers in Downtown Brooklyn. The fund bought a lot on Fulton Street for $19 million a year ago, and its trustees began drawing up plans for a building.

With the value of real estate in Brooklyn rising fast, Mr. Ward said, it became clear that the wisest move would be to build the biggest building possible and rent out the extra space for stores and offices. Rather than have the hotel owners shoulder the estimated $100 million in building costs, the union offered to have its pension fund buy the land and build the building, he said.

The clinic would take up about half of the space and pay rent to the pension fund, which would hope to recoup its investment from the other tenants, Mr. Ward said. He said that in the past year the value of the land had already increased considerably.

The union began presenting the terms of the tentative agreement to its 32,000 members on Tuesday. But they will not vote on it for at least a few months because the federal Department of Labor would have to approve the transaction with the pension fund, Mr. Ward said.

Mr. Ward, who was re-elected to a three-year term as the union’s president in April, called the proposed transaction a “magnificent opportunity” to take advantage of the boom in Brooklyn. Pressed on the possibility that the pension fund could lose money on the venture, Mr. Ward said he saw that possibility as remote, but added, “Maybe I’m overly optimistic.”

Under the deal, the union members’ wages would rise steadily. Under the existing contract, a housekeeper earns $27.41 an hour, or almost $50,000 a year, far more than the current minimum wage in New York of $8 an hour, or even the $15 an hour that some advocates for low-wage workers are pushing for.

The existing contract will take the housekeeper’s pay to almost $60,000 in four years. The extension would add about $9,000, or 15 percent, to that over the next five years.