Timeshares and fractional ownership of homes could be prohibited in parts of Tisbury if voters approve a new zoning bylaw drawn up by the town’s planning board.

The draft bylaw, unveiled earlier this month, aims to shield Tisbury’s housing stock from corporations like Pacaso and Ember, which market one-eighth ownership shares of vacation homes in popular destinations from Napa to Nantucket.

If approved, it would ban timeshares and fractional ownership in the town’s residential districts.

“It’s those commercial platforms and the selling of shares on the open market that’s the primary concern,” said Laura Silber, housing planner for the Martha’s Vineyard Commission, who joined a planning board discussion of the draft bylaw on Feb. 6

San Francisco-based Pacaso, the best-known of at least six fractional-ownership companies that have sprung up in the U.S., Mexico and the European Union, has already begun purchasing homes on Nantucket, where it claims to be unaffected by the town’s ban on time shares because it sells ownership shares, not blocks of time.

Ms. Silber said a Utah firm called Ember poses an even greater risk to the Vineyard’s already unstable housing market.

“Pacaso’s targeting more what’s called the luxury home, $5 million to $7 million properties. Ember is targeting a younger demographic, and they’re targeting more single-family homes in residential neighborhoods,” she said.

“This can become a driving platform for short-term rental investment properties,” Ms. Silber added. “I think regulating this now makes sense.”

Planning board member Elaine Miller agreed.

“I’d like to see it out there as a warning [to the firms]: Don’t jump in right now, because we’re watching you,” Ms. Miller said.

Along with the draft new bylaw, an online public hearing at 5 p.m. Wednesday will also cover several proposed updates to existing bylaws, with multiple changes to the bylaw covering businesses in residential neighborhoods.

The planning board proposes loosening the bylaw’s prohibition on storing business materials outside, as long as the stored materials are screened from neighboring homes and public ways.

The draft update also clarifies that only one commercial vehicle can be parked on the lot.

“A common zoning complaint has been a tradesperson parking multiple work vans or trucks on the lot and then workers report to the home early in the morning to get in their van for the day causing extra noise in residential neighborhoods,” the planning board notes in the draft.

Another proposed bylaw change strikes the requirement that accessory dwellings are allowed only inside existing homes.

Following Wednesday’s hearing, the planning board will finalize language for the articles it will submit to voters on the April 25 town meeting warrant, seeking to update the bylaws.