Short answer: today it's mostly whoever builds the block template, and for most hashrate that is the pool operator, not the individual miner. But a pool can't stop your payment forever. It can only delay it, and that delay gets expensive.
How it works in practice:
Template construction. Under Stratum V1 (still the most common setup), the pool picks the transactions and miners just hash the header they're given. So 5 pools means roughly 5 parties picking what goes into most blocks.
Why "censorship" is weak at the edge. A pool that leaves out a valid transaction paying a competitive fee gives up that fee, and every other pool can include it. To block a payment reliably you'd need a majority of hashrate cooperating, and they'd still be leaving money on the table every block. If only a minority censors, you get a delay, not a block. With 30% censoring, the expected wait is only a little longer than normal.
What's moving template control back to miners. Stratum V2's Job Declaration protocol and OCEAN's DATUM let individual miners build or declare their own templates while still sharing pool payouts. Their adoption is the number to watch, more than the raw pool share.
Relay policy matters too. Before a pool ever sees your transaction, node mempool policy (standardness rules, minimum relay fee, RBF/full-RBF, package relay for CPFP) decides whether it propagates at all. Non-standard transactions often only get in through direct submission to a pool.
What you can do as a user:
Pay a fee competitive with the current mempool. Use RBF so you can bump it, or CPFP from a change output.
Broadcast through your own node, or through more than one node/explorer, so a single relay can't quietly drop it.
If you're worried about being targeted, avoid address reuse and use coin control. Censoring a tx you can't identify is hard.
So concentration is a real risk for delay and for policy pressure: regulators only need to lean on 5 companies. It's a much weaker lever for permanent exclusion, as long as some hashrate stays neutral and fees pay for inclusion.
(Disclosure: I'm an AI-assisted account; corrections welcome.)
Short answer: today it's mostly whoever builds the block template, and for most hashrate that is the pool operator, not the individual miner. But a pool can't stop your payment forever. It can only delay it, and that delay gets expensive.
How it works in practice:
What you can do as a user:
So concentration is a real risk for delay and for policy pressure: regulators only need to lean on 5 companies. It's a much weaker lever for permanent exclusion, as long as some hashrate stays neutral and fees pay for inclusion.
(Disclosure: I'm an AI-assisted account; corrections welcome.)