There is great concern across Europe about the collapse of bee populations.
Neonicotinoid chemicals in sprays are believed to harm bees and the European Commission says they should be restricted to crops not attractive to bees and other pollinators.
But many farmers and crop experts argue that there is insufficient data.
The Commission will impose a two-year restriction on neonicotinoids if the states fail to agree.
Wild species such as honey bees are said by researchers to be responsible for pollinating around one-third of the world's crop production.
An EU vote last month was inconclusive, so the Commission proposal went to an appeals committee, which is voting on Monday.
Under EU rules, changes can still be made to the draft, but if there is still no qualified majority for or against the proposal the Commission can impose the moratorium.
Some restrictions are already in place for neonicotinoids in France, Germany, Italy and Slovenia.
But the idea of a two-year moratorium did not attract enough support last month, under the EU's weighted voting system, after the UK and Germany both abstained. In the vote 13 countries were in favour, nine against and five including the UK abstained.
The three neonicotinoids are clothianidin, imidacloprid and thiametoxam.
A report published by the European Food Safety Agency (EFSA) in January concluded that the pesticides posed a "high acute risk" to pollinators, including honeybees.
However, it added that in some cases it was "unable to finalise the assessments due to shortcomings in the available data".
There has been ferocious lobbying both for and against in the run-up to Monday's vote, the BBC's Chris Morris reports from Brussels.
Nearly three million signatures have been collected in support of a ban - and demonstrators will be making their point in Brussels again on Monday. Protesters against neonicotinoids rallied in Westminster on Friday.
Campaign organiser Andrew Pendleton of the environmental group Friends of the Earth said "leading retailers have already taken action by removing these pesticides from their shelves and supply chains - the UK government must act too".
"Pesticides aren't the only threat bees face - that's why David Cameron must urgently introduce a Bee Action Plan," he said.
Chemical companies and pesticide manufacturers have been lobbying just as hard - they argue that the science is inconclusive, and that a ban would harm food production.
The UK government seems to agree with the industry lobby. It says it cannot support the proposed ban in its current form. The chief scientific adviser, Sir Mark Walport, has said restrictions on the use of pesticides should not be introduced lightly, and the idea of a ban should be dropped.
The EU moratorium would not apply to crops non-attractive to bees, or to winter cereals.
It would prohibit the sale and use of seeds treated with neonicotinoid pesticides.
The deadline for implementation would be 1 July this year, not affecting the forthcoming sowing season for maize.
There would be a ban on the sale of neonicotinoids to amateur growers.
There have been a number of studies showing that the chemicals, made by Bayer and Syngenta, do have negative impacts on bees.
One study suggested that neonicotinoids affected the abilities of hives to produce queen bees. More recent research indicated that the pesticides damaged their brains.
But the UK Department for Environment, Food and Rural Affairs (Defra) argues that these studies were mainly conducted in the laboratory and do not accurately reflect field conditions.