Prime minister Mark Rutte is attempting to blackmail voters by warning them to save up next year for an extra tax bill, if the senate votes down the government’s tax reform plans, says a D66 MP.

Kees Verhoeven told NPO radio on Saturday the prime minister was guilty of ‘political blackmail’ in telling voters they may need to pay an extra tax demand in 2017 because they will not have paid enough tax next year..

Rutte made the comments on Friday after it emerged that the tax office has already taken the impact of the reforms into account in calculating next year’s preliminary tax demands. This means up to four million people could have to pay a surcharge if income tax rates and other allowances are not adjusted as expected.

Verhoeven said ‘chaos at the tax office’ and ministerial panic were the reasons why Rutte made his statement.

Although the reforms, which include €5bn worth of income tax cuts, have been approved in the lower house of parliament, there is no majority support in the upper house. The senate vote has been delayed to mid December to give ministers more time to reach a compromise.

D66 is one of the opposition parties which is refusing to back the plan.