Funds collected will be refunded and not kept by the government:

> Each resident in Austria will get an annual reimbursement, with the exact amount determined by where they live to ensure those in rural regions without good public transport don’t lose out. Children are entitled to half their parents’ amount — so a family of two adults and two children in Vienna could expect to get 300 euros ($358) for example.

While the term "tax" is used proverbially, if the government does not keep the money, it is actually a tax?

This was a constitutional question in Canada, and the majority of the Supreme Court ruled that it was not:

> As a final matter, the fuel and excess emission charges imposed by the GGPPA have a sufficient nexus with the regulatory scheme to be considered constitutionally valid regulatory charges. To be a regulatory charge, as opposed to a tax, a governmental levy with the characteristics of a tax must be connected to a regulatory scheme. The first step is to identify the existence of a relevant regulatory scheme; if such a scheme is found to exist, the second step is to establish a relationship between the charge and the scheme itself. Influencing behaviour is a valid purpose for a regulatory charge and regulatory charges need not reflect the cost of the scheme. The amount of a regulatory charge whose purpose is to alter behaviour is set at a level designed to proscribe, prohibit, or lend preference to a behaviour. Limiting such a charge to the recovery of costs would be incompatible with the design of a scheme of this nature. Nor must the revenues that are collected be used to further the purposes of the regulatory scheme. Rather, the required nexus with the scheme will exist where the charges themselves have a regulatory purpose. There is ample evidence that the fuel and excess emission charges imposed by Parts 1 and 2 of the GGPPA have a regulatory purpose. They cannot be characterized as taxes; rather, they are regulatory charges whose purpose is to advance the GGPPA’s regulatory purpose by altering behaviour.

[…]

> [219] In the instant case, there is ample evidence that the fuel and excess emission charges imposed by Parts 1 and 2 of the GGPPA have a regulatory purpose. Ontario does not assert, nor would such an assertion be supportable, that the levies in this case amount to disguised taxation. The GGPPA as a whole is directed to establishing minimum national standards of GHG price stringency to reduce GHG emissions, not to the generation of revenue. As Richards C.J.S. aptly observed, the GGPPA “could fully accomplish its objectives . . . without raising a cent”: para. 87. This is true of both Part 1 and Part 2. The levies imposed by Parts 1 and 2 of the GGPPA cannot be characterized as taxes; rather, they are regulatory charges whose purpose is to advance the GGPPA’s regulatory purpose by altering behaviour. The levies are constitutionally valid regulatory charges.

* https://www.canlii.org/en/ca/scc/doc/2021/2021scc11/2021scc1...

* https://en.wikipedia.org/wiki/Greenhouse_Gas_Pollution_Prici...

Canada is a federation, and the national and provincial governments each have their areas of responsibility. There were challenges whether there was federal over reach, and the court said there was not given the structure of the legislation.

* https://elc.ab.ca/i-read-the-carbon-tax-decision-so-you-dont...