Health insurers have reduced the benefits on a number of plans and withdrawn some schemes, prompting experts to warn people who auto-renew may lose out.
Some of the changes will mean people having to pay up to €3,000 for the likes of a hip operation, Dermot Goode of TotalHealthCare.ie said.
He said Laya Healthcare was the latest to introduce co-payments on major orthopaedic and ophthalmic procedures when carried out in private hospitals.
A co-payment is a shortfall in what is reimbursed by the insurer, with this amount having to be paid by the consumer.
Laya has introduced co-payments on its popular 360 Care and 360 Care Select plans. From this month it is bringing in a 20pc shortfall payment for these procedures in a private hospital.
Mr Goode said this was a significant change to the cover and could leave members with a shortfall of up to €3,000 for the likes of a hip or knee replacement.
Laya has also introduced a similar change to its Simply Health Choice semi-private corporate plan.
"Many of those receiving their renewal notices may not read the documents sufficiently to appreciate the reduction in cover, particularly older members who may have opted for these plans specifically to have this full cover in place," Mr Goode said.
He said Vhi and Irish Life Health had similar shortfalls already on many of their corporate plans.
And Vhi has now withdrawn its popular Health Plus Choice plan, which had cost €2,950, and the Forward Plan Level 1 scheme, which was €3,270. It has replaced them with a plan called AdvancedCare Extra with Day-to-Day, costing €3,080 per adult.
Mr Goode said if an insurer retired a plan and replaced it with a more expensive option, members should never automatically transfer to the new scheme without checking the alternatives.
He said there were alternatives costing from €1,550 to €2,400 per adult that should be considered.
Laya said it regularly reviewed products and prices. Vhi had no comment.