Word, phrase or idiom for enforced charity?

Like when you must pay for a plastic carry bag for your shopping in a superstore but it all goes to charity. Little contrived inconveniences designed to extract money from you. There must be a specific term to capture this phenomenon of soft enforcement?

Tithe is an excellent suggestion. Another alternative is earning to give.

tzedaka(h) is a Jewish term for obligatory charity.

zakat is a complementary Islamic term.

Tithe comes to mind

A tithe (/ˈtaɪð/; from Old English: teogoþa "tenth") is a one-tenth part of something, paid as a contribution to a religious organization or compulsory tax to government. Today, tithes are normally voluntary and paid in cash, cheques, or stocks, whereas historically tithes were required and paid in kind, such as agricultural products. Several European countries operate a formal process linked to the tax system allowing some churches to assess tithes.

Other suggestions could be

Alternative giving or Pay it forward

I have sometimes seen "suggested contribution", or "recommended donation" used for this.

An example would be that in the UK, (at least in London) the museums are free for anyone who desires to go in. However, they have a 'suggested contribution' for each museum that is about what you would expect to pay for the price of a ticket.

It's not enforced per se, but they do have many signs and donation boxes where they have signs bearing language like 'suggested donation' or 'suggested contribution'.