It's time to register your protest at the biggest cut to private and public sector pensions in British history. By linking future pension increases to the consumer price index (CPI) rather than retail prices (RPI), the government this April slashed pensions payments by at least 15% over every worker's lifetime.

You can now sign an online petition to the House of Commons objecting to this move - and if more than 100,000 people sign up the subject is eligible for debate in the Commons.

Go to http://epetitions.direct.gov.uk/petitions/1535 and make sure the RPI-CPI switch – which was made without consultation or negotiation of any kind - is debated in parliament. At the time of writing, 17,000 people had already signed.

Prospect has campaigned against the switch from the day it was announced. It affects every pension scheme in the private sector that does not specifically guarantee to link pension increases to RPI, and every scheme in the public sector.

Prospect is one of six trade unions and pensioner organisations that has challenged the CPI switch in the High Court. We argue that CPI is not a fair measure of the cost of living for pensioners since it measures changes in consumer behaviour (ie trading down to cheaper goods) rather than price increases for the same goods.

CPI also excludes housing costs, which the government maintains most pensioners do not incur since they already own their home outright.

The unions' application for a judicial review is scheduled to be heard in court on October 25.

Prospect has produced a video briefing on the RPI-CPI switch.

You can find out how the government e-petitions site works here.