More than 100 MPs are urging the health secretary, Matt Hancock, to provide stronger assurances that social care workers forced to drop shifts because of the coronavirus pandemic will receive adequate sick pay.

NHS England issued guidance advising trusts to give full sick pay to staff who have to self-isolate because of the disease, but there is growing concern nearly 400,000 carers on zero-hours contracts may miss out.

There are fears that carers, who earn little more than £8 an hour on average in the private sector, may turn up for work when they are unwell to avoid losing pay because of illness or self-isolation.

Statutory sick pay (SSP), worth £94.25 a week, kicks in after workers have been off for four consecutive days. Though the UK chancellor, Rishi Sunak, announced in the budget on Wednesday that SSP would be extended to start on day one, an open letter signed by more than 100 MPs says many carers working irregular hours will be unable to prove they earn above the threshold of £118 a week to qualify for the payment. Meanwhile, the letter highlights, those who do receive SSP while self-isolating will take home far less than they would in a normal week meaning it will cause “significant financial hardship for them and their families”.

The care sector has notoriously perilous pay instability, with a Guardian investigation previously exposing how a major UK firm fined workers £50 if they phoned in sick.

The letter welcomes NHS England advising trusts to: “Ensure that any member of staff, including bank staff and subcontractors, who has to be physically present at an NHS facility to carry out their duties, receives full pay for any period in which they are required to self-isolate as a result of public health advice.”

The MPs call on the guidance to be extended to all care workers to “ensure care workers will not face financial detriment if they contract Covid-19, but it will help to delay the virus from spreading within care homes and amongst vulnerable people, potentially saving lives.”

Labour MP Helen Hayes who organised the letter – also signed by the shadow minister for health and social care Barbara Keeley – said: “Social care staff work incredibly hard all year round to support older people and working-age adults who have care needs. Many of those who receive care will also be in high-risk categories for coronavirus, and it is vital that social care staff are given the advice and support to enable them to continue to work while minimising the risk of infection both to themselves and the vulnerable people in their care.

“Currently, care workers on zero-hours contracts are not being granted the same access to sick pay as NHS bank staff and subcontractors. NHS trusts have been advised to pay all staff in full in order to ensure that they self-isolate when necessary. Social care workers who are advised to self-isolate face the difficult choice of financial hardship or continuing to work and risk passing on the coronavirus to their patients. The government must urgently address this and provide the funding to prevent a public health emergency in the social care sector.”

A Government spokesman said: “Just yesterday we published new guidance for the social care sector to make sure older people and those with pre-existing conditions and care needs are supported.

“As part of the government’s emergency legislation measures, Statutory Sick Pay will be available from day one for those affected by coronavirus. Anyone on zero-hour contracts who may not be eligible for Statutory Sick Pay will be able to claim Universal Credit or New Style Employment and Support Allowance, dependent on their circumstances.”