MOSCOW, April 29 (Reuters) - Russians’ real disposable incomes declined 3.6% year on year in the first quarter and fell 26.7% compared with the fourth quarter of 2020, data showed on Thursday, highlighting lingering issue with living standards ahead of parliamentary elections. For years, President Vladimir Putin has promised to raise real disposable incomes, a measure of people’s purchasing power and one of Russia’s most socially sensitive issues. Yet the pandemic coupled with low oil prices saw incomes falling each quarter from the second quarter of 2020 when it staged the deepest decline in decades. Real disposable incomes, which are inflation-adjusted incomes that exclude mandatory payments, fell 3% in 2020 even though the average salary paid rose 6% to 51,083 roubles ($685), according to the Federal Statistics Service, or Rosstat. The economy shrank 3% last year, its sharpest contraction in 11 years, and inflation hit 5.8% last month, its highest level since 2016. Addressing falling living standards is one of the priorities for Putin before a parliamentary election due in September. The economy ministry expects real disposable incomes to grow by 3% in 2021. ($1 = 74.5627 roubles) (Reporting by Andrey Ostroukh; Editing by Toby Chopra)