Migrant workers and the UK’s largest union will carry out a mass leafleting campaign in Shabana Mahmood’s Birmingham constituency to protest against a planned change in immigration policy.

The Labour-affiliated Unison union says the changes will adversely affect migrant care workers. About one-third of all care workers and one-fifth of all NHS workers are migrants.

The union raised particular concerns about the planned doubling of time before migrant care workers could apply for settlement in the UK, from five to 10 years.

Union members hope to leaflet about one-third of the home secretary’s approximately 55,000 constituents in the Ladywood area of the city. Union sources say it is the first time such a large Labour-affiliated union is lobbying en masse against a key party policy.

Although the earned settlement proposals, which have been outlined in a white paper, call for a doubling of settlement time to 10 years, in some cases migrants may have to wait longer than that if they entered the UK illegally or have claimed benefits here. A consultation on the proposals ended in February and attracted 200,000 responses.

The union is also calling for a change to sponsorship rules for these visas. At the moment, these workers must be sponsored by their employer, which officials say can lead to exploitation. There are calls for this to be replaced with a sponsorship scheme managed by a public-sector body.

The mass leafleting campaign is taking place a day before a national day of action on Friday, which is part of the union’s Fair Visas Now campaign. Workers will be lobbying their constituency MPs, particularly Labour ones, to raise concerns about the earned settlement proposals.

One migrant care worker taking part in the campaign has a degree and postgraduate qualifications and is a qualified accountant and an accredited fraud investigator. She says she is doing care work because she wants to give back to British society.

She said she was devastated by the planned extension. “We had a legitimate expectation that we could apply to settle here after five years. Somebody gave the home secretary wings to allow her to fly. She should allow the same for our children. I hope she will hear our voices.”

A second migrant care worker involved in the campaign said the new rules were “affecting me and my family greatly”. He said: “I work as a carer for people with disabilities. I love my work because it is an opportunity to give back to humanity. I felt devastated when I heard about the proposed changes. British people are known for their compassion. We urge the home secretary to show compassion in this situation. We have had the rug pulled from under our feet.”

Unison’s general secretary, Andrea Egan, said: “Social care is already under immense strain, with tens of thousands of vacancies. The sector’s been reliant on overseas staff willing to do this essential work, but the home secretary is closing the door on them. Extending the qualifying period risks driving experienced, committed staff out of the sector altogether.

“If the government’s serious about fixing social care, it must match its ambitions on pay and standards with fair treatment for the workforce. But the best way to start is by scrapping these cruel, unnecessary proposals.”

A Home Office spokesperson said: “We will always welcome those that come to this country and contribute to our national life. But the privilege of living here forever should be earned, not automatic.

“Between 2021 and 2024, this country experienced levels of migration it had historically seen over four decades. We must be honest about the scale and impact of hundreds of thousands of low-skilled migrants getting settlement.

“The government will double the route to settlement from five to 10 years. As announced in November, we are consulting to apply this change to those in the UK today who have not received settled status. We are reviewing the 200,000 responses and will outline our response in due course.”