EAST Riding Council leader Stephen Parnaby is urging residents living close to Hull to reject the idea of expanding the city's boundaries.
He spoke out ahead of Friday's deadline for eligible voters in 12 parishes to return ballot papers in the referendum organised by his authority.
About 70,000 people can vote in the East Riding poll.
The result is not binding and Hull City Council has not even put forward formal proposals to extend its boundaries in parts of the East Riding.
Instead, the option is one of a number being examined by a Hull-commissioned independent inquiry looking at local government reorganisation in the area.
But Cllr Parnaby is hoping a big "no" vote will send out a clear message over the boundary issue.
He said: "I would urge everyone who has been sent a ballot paper to make their voice heard on this important issue.
"We have been criticised by Hull councillors for holding this referendum, but we believe it is right and proper to have a democratic process and to let our residents have a say on whether they want to be part of the East Riding or Hull.
"Hull City Council has not once consulted us about its plans.
"It is a hostile land-grab and I hope East Riding residents send out a resounding no to becoming part of an expanded Hull."
As well as a question over the idea of an extended Hull, people are also being asked whether they think the city council should be allowed to build on land it owns in the East Riding.
The latter question does not mention specific sites, but the two councils have clashed recently over future land allocation policies at sites near Hedon and Cottingham that are owned by Hull.
The city council has lodged formal objections to draft allocations published by the East Riding as part of its proposed new Local Plan.
The former Hedon aerodrome site near Saltend is a particular bone of contention between the two authorities, with Hull keen to encourage new development on the land to attract new jobs and major investment.
The city's objections are expected to be heard in detail at a public examination of the East Riding's Local Plan proposals due to be held next month.
Meanwhile, city council leader Councillor Steve Brady has criticised the East Riding referendum for asking the wrong questions at the wrong time.
He said: "The questions are so simplistic. I find it quite unbelievable that serious politicians have actually put them forward in the first place.
"People should be being asked whether they want more opportunities and better prospects for their children and their families.
"As for trying to build on green spaces, no one seems to be saying anything about the green spaces currently being built on in Beverley and Hessle."
The ballot forms have to be returned by Friday afternoon.
Ballot result to be declared on MondayTHE result of the East Riding Council referendum is expected to be announced on Monday.
Ballot forms have to be returned by Friday afternoon.
They can be sent via Freepost or dropped into ballot boxes at council customer service centres.
People living in 12 parishes have had the chance to vote since earlier this month.
Those involved are Anlaby with Anlaby Common, Bilton, Cottingham, Elloughton cum Brough, Hedon, Hessle, Kirk Ella, North Ferriby, Preston, Swanland, Welton and Willerby.
The area taking part in the vote was chosen by the East Riding because it reflects one of the options being examined by the Hull inquiry, namely extending the city's boundary to cover the so-called Hull travel-to-work area.
People living elsewhere in the East Riding are also being asked their views through a consultation in the council's in-house magazine.
Once the ballot votes are counted on Monday, the results of both polls will be announced.
