The UK government says it will consider a unilateral ban on plastic microbeads in shower gels and facial scrubs if the EU doesn't prohibit their use.
Several nations, including the US, have already banned microbeads in cosmetics because of their impact on marine life.
The beads are used in products to exfoliate the skin - but they are swelling plastic debris in the ocean.
Scientists say a ban on the tiny beads wouldn't solve plastic pollution, but it is an easy place to start.
The Environment Minister Rory Stewart told the Commons on Thursday: "If we cannot get a common position out of the European Union, we are open to the possibility of the UK acting unilaterally."
The move was welcomed by Greenpeace, which has campaigned against plastic pollution.
"This is reflective of the opinion of hundreds of thousands of people across the country," said the organisation's oceans campaigner Louise Edge. "But any legislation would need to go further than that brought in by the Obama administration in the US, which only covers certain types of microbeads."
The problem is that microbeads are so tiny they slip through water treatment works and enter the ocean, where they are ingested by fish and other creatures.
The beads get stuck in creatures' stomachs and can be toxic in large quantities.
The government had previously asked firms to phase them out on a voluntary basis. That process is already under way at Unilever, and L'Oreal says it will follow by next year.
MPs on the Environmental Audit Committee are due to start hearings on microplastics on Monday.
Prof Richard Thompson from Plymouth University told the committee in written evidence that one third of 504 fish tested from the English Channel had plastic in their digestive tract - although the average was less than two pieces of microplastic.
He said some seabirds have been shown to ingest larger quantities, and microplastics have been found to harm worms that are at the bottom of the food chain.
Dr Erik Sebille from Imperial College London said microbeads make up a very low proportion of plastics in use, so they probably make just a small contribution to the total plastic waste in the ocean.
That means banning microbeads would have a relatively small impact on the problem. But Dr Sebille said: "A ban is about taking action to tackle ocean plastic pollution at its source - and this is the right way to address the problem."
Both academics say understanding the impact of ocean plastics on marine life is still in its early stages.
Follow Roger on Twitter