A group of politicians are threatening legal action unless Boris Johnson orders an independent investigation into Russian interference in elections.
The letter signed by Green MP Caroline Lucas and Labour's Chris Bryant follows a report which said the UK "badly underestimated" the Russian threat.
The parliamentarians argue the prime minister's "lack of action" breaches the right to free elections.
The government said the UK had "robust systems" to protect elections.
In July, Parliament's Intelligence and Security Committee published a long-awaited report into Russian activity in the UK including disinformation campaigns, cyber warfare and the targeting of Russian expatriates in the UK.
It claimed the government made no effort to investigate Russian interference in the 2016 EU referendum and called for "immediate action" including "an assessment of potential Russian interference" in the Brexit vote.
UK 'badly underestimated' Russian threat
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US intelligence chiefs have accused Russia of interfering in the 2016 presidential election and earlier this month they warned that China, Russia and Iran were among the countries seeking to influence this year's vote.
Now a group of MPs and peers in the UK say they will take the prime minister to court if he refuses to take "essential steps to protect future elections".
https://www.bbc.co.uk/news/uk-politics-53862369