Do anti-poverty programs raise marginal tax rates?

Yes, according to this US study. Subject to caveats:

we calculate the effective average marginal tax rate if this household increases its income from $10,000 to $40,000. That is, how much of the additional $30,000 of earnings is lost to government through direct taxes or loss of benefits? The average marginal tax rate in the first bar of Table 3, 29 percent, is based simply on federal and state direct taxes, including Social Security and the EITC. The rate rises appreciably as the family enrolls in additional transfer programs in bars 2 and 3. For a family enrolled in all the more universal non-wait-listed programs like SNAP, Medicaid, and SCHIP, the average effective marginal tax rate could be 55 percent. Enrolling the family in additional waitlisted programs, like housing assistance and TANF, ratchets the rate up above 80 percent....