Mid-America Apartment Communities Inc. is close to agreeing to a merger with Post Properties Inc., a source familiar with the matter said on Sunday.

The $4 billion deal is expected to be announced Monday and would create the largest publicly traded multifamily apartment real estate investment trust by number of units, said the source, who was not authorized to speak publicly about the matter.

For each share of Post Properties stock, shareholders would receive 0.71 share of newly issued MAA stock, the source said.

The deal would combine companies buoyed by the rising demand for rental properties, creating an entity with more than 300 properties and 100,000 units, with a sizable presence in fast-growing metropolitan areas in Texas and Georgia, the source said.