BUENOS AIRES (Reuters) - Argentina s President Mauricio Macri vowed to press ahead with reforms to the country s tax, labor and retirement systems in a speech on Monday, a week after his  Let s Change  coalition swept to victory at the polls in midterm elections. The government will present a tax reform proposal this Tuesday or Wednesday, and an amnesty plan for companies that hired workers informally in the coming days, Macri said. He added that the government would convene a commission to propose changes to the retirement system in coming weeks. The speech marked a roadmap for the second half of Macri s four-year term, as he seeks to implement business-friendly reforms to attract investors who avoided the country during more than a decade of populist rule.   We need lower taxes, more public works, and all this we need to achieve with fiscal balance,  Macri told a gathering of lawmakers, governors, union leaders, judges and others. Investors have been encouraged by the reforms Macri has implemented since taking office in December 2015, including lifting foreign exchange controls, settling with holdout creditors, and lowering export taxes. But significant investment has not arrived. Companies have demanded lower costs, while credit agencies are concerned about a deep fiscal deficit.  Macri s coalition swept the five most populous areas in  midterm elections, giving him a broader mandate to pass reforms, though it still lacks majorities in both chambers of Congress. Macri said his government had reduced the country s tax burden, and wanted to make the system  simpler, clearer, and fairer.   He reiterated the government s aim of slashing Argentina s fiscal deficit by one percentage point of gross domestic product per year. And he also vowed to reform the country s retirement system, a large driver of government spending.   We need to start a mature and honest conversation about our retirement and pension system,  Macri said.  Our retirement system hides serious inequities, and it is not sustainable.   While Macri has said he does not plan major changes to the country s labor code, he has said the government plans to provide incentives to companies to formalize undeclared workers and work with unions in specific sectors to lower costs. Macri also pledged reforms to the country s justice system to combat corruption. Cabinet Chief Marcos Pena told journalists that the resignation on Monday of chief prosecutor Alejandra Gils Carbo, appointed during the former administration of President Cristina Fernandez, was a step towards making the judiciary more independent. 