。
The opposition party submitted an income-tax-reduction bill.
Literal
Opposition-party [topic-は] income-tax reduction bill [obj-を] submitted.
所得税減税法案 is a heavy compound: 所得税 ('income tax') + 減税 ('tax reduction') + 法案 ('bill, draft law'). Compound nouns of this kind are typical of political, legal, and economic news in Japanese — nouns stack freely to form specific concepts. 提出する ('submit, present') is the formal verb for filing or introducing documents, bills, reports.