UEFA is withholding Champions League and Europa League prize money from six clubs over unpaid debts.
UEFA says they are Astra Ploiesti, Metalurh Donetsk, Hajduk Split, HSK Zrinjski, Skonto Riga and Trabzonspor.
Another 25 clubs, which UEFA did not name, must provide further information about apparent financial problems. All 31 have a Sept. 30 deadline.
The cases involve "overdue payables," involving late payments of transfer fees, wages and social taxes.
UEFA says the provisional sanctions "remain in force until all identified balances have been settled in full," or its club finance panel gives final verdicts.
UEFA says the hundreds of clubs it monitors owed $12.2 million in overdue payments by June 2013, compared to $77 million two years ago.